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 $104.83   11.656%   $117.049   $117.05   $117.05   $117.00  
  Purchase #2 $110.83   13.731%   $126.0481   $126.05   $126.05   $126.00  
  Purchase #3 $151.67   4.460%   $158.4345   $158.43   $158.45   $158.40  
  Purchase #4 $221.81   3.225%   $228.9634   $228.96   $228.95   $229.00  
  Purchase #5 $46.38   10.628%   $51.3093   $51.31   $51.30   $51.30  
  Purchase #6 $189.75   4.772%   $198.8049   $198.80   $198.80   $198.80  
  Purchase #7 $89.68   6.461%   $95.4742   $95.47   $95.45   $95.50  
  7 purchase totals = $914.95       $976.0834   $976.07   $976.05   $976.00