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 $206.61   13.343%   $234.178   $234.18   $234.20   $234.20  
  Purchase #2 $29.63   13.447%   $33.6143   $33.61   $33.60   $33.60  
  Purchase #3 $113.98   8.180%   $123.3036   $123.30   $123.30   $123.30  
  Purchase #4 $86.41   13.220%   $97.8334   $97.83   $97.85   $97.80  
  Purchase #5 $147.71   4.453%   $154.2875   $154.29   $154.30   $154.30  
  Purchase #6 $156.54   4.796%   $164.0477   $164.05   $164.05   $164.00  
  Purchase #7 $149.68   11.424%   $166.7794   $166.78   $166.80   $166.80  
  7 purchase totals = $890.56       $974.0439   $974.04   $974.10   $974.00