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 $62.34   9.757%   $68.4225   $68.42   $68.40   $68.40  
  Purchase #2 $60.31   9.116%   $65.8079   $65.81   $65.80   $65.80  
  Purchase #3 $106.26   8.303%   $115.0828   $115.08   $115.10   $115.10  
  Purchase #4 $91.65   8.724%   $99.6455   $99.65   $99.65   $99.60  
  Purchase #5 $206.38   3.835%   $214.2947   $214.29   $214.30   $214.30  
  Purchase #6 $41.79   4.832%   $43.8093   $43.81   $43.80   $43.80  
  Purchase #7 $66.84   11.186%   $74.3167   $74.32   $74.30   $74.30  
  7 purchase totals = $635.57       $681.3794   $681.38   $681.35   $681.30