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 $95.65   3.192%   $98.7031   $98.70   $98.70   $98.70  
  Purchase #2 $6.71   8.104%   $7.2538   $7.25   $7.25   $7.30  
  Purchase #3 $158.99   12.154%   $178.3136   $178.31   $178.30   $178.30  
  Purchase #4 $171.56   13.869%   $195.3537   $195.35   $195.35   $195.40  
  Purchase #5 $202.62   13.237%   $229.4408   $229.44   $229.45   $229.40  
  Purchase #6 $119.43   6.121%   $126.7403   $126.74   $126.75   $126.70  
  Purchase #7 $147.30   5.685%   $155.674   $155.67   $155.65   $155.70  
  7 purchase totals = $902.26       $991.4793   $991.46   $991.45   $991.50