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 $60.77   12.465%   $68.345   $68.35   $68.35   $68.30  
  Purchase #2 $239.25   10.378%   $264.0794   $264.08   $264.10   $264.10  
  Purchase #3 $149.34   12.598%   $168.1539   $168.15   $168.15   $168.20  
  Purchase #4 $188.90   4.198%   $196.83   $196.83   $196.85   $196.80  
  Purchase #5 $67.81   9.201%   $74.0492   $74.05   $74.05   $74.00  
  Purchase #6 $186.57   11.238%   $207.5367   $207.54   $207.55   $207.50  
  Purchase #7 $51.37   3.853%   $53.3493   $53.35   $53.35   $53.30  
  7 purchase totals = $944.01       $1,032.3435   $1,032.35   $1,032.40   $1,032.20