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 $88.70   7.244%   $95.1254   $95.13   $95.15   $95.10  
  Purchase #2 $206.25   6.163%   $218.9612   $218.96   $218.95   $219.00  
  Purchase #3 $123.39   3.352%   $127.526   $127.53   $127.55   $127.50  
  Purchase #4 $202.84   12.160%   $227.5053   $227.51   $227.50   $227.50  
  Purchase #5 $22.99   5.715%   $24.3039   $24.30   $24.30   $24.30  
  Purchase #6 $170.75   11.167%   $189.8177   $189.82   $189.80   $189.80  
  Purchase #7 $26.80   8.479%   $29.0724   $29.07   $29.05   $29.10  
  7 purchase totals = $841.72       $912.3119   $912.32   $912.30   $912.30