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 $176.58   5.303%   $185.944   $185.94   $185.95   $185.90  
  Purchase #2 $58.68   11.399%   $65.3689   $65.37   $65.35   $65.40  
  Purchase #3 $247.52   6.809%   $264.3736   $264.37   $264.35   $264.40  
  Purchase #4 $48.64   12.420%   $54.6811   $54.68   $54.70   $54.70  
  Purchase #5 $65.71   4.739%   $68.824   $68.82   $68.80   $68.80  
  Purchase #6 $47.96   9.510%   $52.521   $52.52   $52.50   $52.50  
  Purchase #7 $193.96   6.650%   $206.8583   $206.86   $206.85   $206.90  
  7 purchase totals = $839.05       $898.5709   $898.56   $898.50   $898.60