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 $210.53   8.178%   $227.7471   $227.75   $227.75   $227.70  
  Purchase #2 $22.26   10.268%   $24.5457   $24.55   $24.55   $24.50  
  Purchase #3 $140.28   5.615%   $148.1567   $148.16   $148.15   $148.20  
  Purchase #4 $198.49   11.424%   $221.1655   $221.17   $221.15   $221.20  
  Purchase #5 $60.53   6.765%   $64.6249   $64.62   $64.60   $64.60  
  Purchase #6 $183.70   5.695%   $194.1617   $194.16   $194.15   $194.20  
  Purchase #7 $144.37   11.397%   $160.8238   $160.82   $160.80   $160.80  
  7 purchase totals = $960.16       $1,041.2254   $1,041.23   $1,041.15   $1,041.20