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 $62.54   9.288%   $68.3487   $68.35   $68.35   $68.30  
  Purchase #2 $169.45   13.187%   $191.7954   $191.80   $191.80   $191.80  
  Purchase #3 $99.53   13.637%   $113.1029   $113.10   $113.10   $113.10  
  Purchase #4 $102.80   5.597%   $108.5537   $108.55   $108.55   $108.60  
  Purchase #5 $232.46   13.706%   $264.321   $264.32   $264.30   $264.30  
  Purchase #6 $220.25   9.530%   $241.2398   $241.24   $241.25   $241.20  
  Purchase #7 $39.74   4.606%   $41.5704   $41.57   $41.55   $41.60  
  7 purchase totals = $926.77       $1,028.9319   $1,028.93   $1,028.90   $1,028.90