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 $91.28   12.424%   $102.6206   $102.62   $102.60   $102.60  
  Purchase #2 $130.30   7.162%   $139.6321   $139.63   $139.65   $139.60  
  Purchase #3 $59.36   12.144%   $66.5687   $66.57   $66.55   $66.60  
  Purchase #4 $13.59   7.464%   $14.6044   $14.60   $14.60   $14.60  
  Purchase #5 $160.30   8.120%   $173.3164   $173.32   $173.30   $173.30  
  Purchase #6 $157.65   9.474%   $172.5858   $172.59   $172.60   $172.60  
  Purchase #7 $26.84   5.706%   $28.3715   $28.37   $28.35   $28.40  
  7 purchase totals = $639.32       $697.6995   $697.70   $697.65   $697.70