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 $193.81   12.303%   $217.6544   $217.65   $217.65   $217.70  
  Purchase #2 $113.56   11.269%   $126.3571   $126.36   $126.35   $126.40  
  Purchase #3 $102.52   4.209%   $106.8351   $106.84   $106.85   $106.80  
  Purchase #4 $184.88   11.822%   $206.7365   $206.74   $206.75   $206.70  
  Purchase #5 $117.28   12.170%   $131.553   $131.55   $131.55   $131.60  
  Purchase #6 $37.59   12.580%   $42.3188   $42.32   $42.30   $42.30  
  Purchase #7 $116.90   11.515%   $130.361   $130.36   $130.35   $130.40  
  7 purchase totals = $866.54       $961.8159   $961.82   $961.80   $961.90