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 $116.55   8.380%   $126.3169   $126.32   $126.30   $126.30  
  Purchase #2 $55.84   10.704%   $61.8171   $61.82   $61.80   $61.80  
  Purchase #3 $121.88   11.513%   $135.912   $135.91   $135.90   $135.90  
  Purchase #4 $237.45   13.137%   $268.6438   $268.64   $268.65   $268.60  
  Purchase #5 $39.59   6.837%   $42.2968   $42.30   $42.30   $42.30  
  Purchase #6 $100.74   11.851%   $112.6787   $112.68   $112.70   $112.70  
  Purchase #7 $145.50   5.624%   $153.6829   $153.68   $153.70   $153.70  
  7 purchase totals = $817.55       $901.3482   $901.35   $901.35   $901.30