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 $212.46   8.301%   $230.0963   $230.10   $230.10   $230.10  
  Purchase #2 $5.51   3.792%   $5.7189   $5.72   $5.70   $5.70  
  Purchase #3 $155.29   6.112%   $164.7813   $164.78   $164.80   $164.80  
  Purchase #4 $205.65   10.175%   $226.5749   $226.57   $226.55   $226.60  
  Purchase #5 $59.34   4.400%   $61.951   $61.95   $61.95   $62.00  
  Purchase #6 $168.73   9.869%   $185.382   $185.38   $185.40   $185.40  
  Purchase #7 $46.71   11.414%   $52.0415   $52.04   $52.05   $52.00  
  7 purchase totals = $853.69       $926.5459   $926.54   $926.55   $926.60