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 $64.71   13.847%   $73.6704   $73.67   $73.65   $73.70  
  Purchase #2 $177.36   7.501%   $190.6638   $190.66   $190.65   $190.70  
  Purchase #3 $219.80   5.303%   $231.456   $231.46   $231.45   $231.50  
  Purchase #4 $24.79   6.663%   $26.4418   $26.44   $26.45   $26.40  
  Purchase #5 $24.64   6.491%   $26.2394   $26.24   $26.25   $26.20  
  Purchase #6 $45.62   5.237%   $48.0091   $48.01   $48.00   $48.00  
  Purchase #7 $93.66   9.763%   $102.804   $102.80   $102.80   $102.80  
  7 purchase totals = $650.58       $699.2845   $699.28   $699.25   $699.30