Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $49.84   7.652%   $53.6538   $53.65   $53.65   $53.70  
  Purchase #2 $171.46   12.767%   $193.3503   $193.35   $193.35   $193.40  
  Purchase #3 $234.72   12.154%   $263.2479   $263.25   $263.25   $263.20  
  Purchase #4 $249.38   6.105%   $264.6046   $264.60   $264.60   $264.60  
  Purchase #5 $154.30   11.796%   $172.5012   $172.50   $172.50   $172.50  
  Purchase #6 $247.30   12.474%   $278.1482   $278.15   $278.15   $278.10  
  Purchase #7 $205.35   12.572%   $231.1666   $231.17   $231.15   $231.20  
  7 purchase totals = $1,312.35       $1,456.6726   $1,456.67   $1,456.65   $1,456.70