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 $19.83   11.175%   $22.046   $22.05   $22.05   $22.00  
  Purchase #2 $91.38   10.177%   $100.6797   $100.68   $100.70   $100.70  
  Purchase #3 $11.65   3.134%   $12.0151   $12.02   $12.00   $12.00  
  Purchase #4 $25.71   11.151%   $28.5769   $28.58   $28.60   $28.60  
  Purchase #5 $118.89   9.567%   $130.2642   $130.26   $130.25   $130.30  
  Purchase #6 $61.27   4.485%   $64.018   $64.02   $64.00   $64.00  
  Purchase #7 $15.76   3.791%   $16.3575   $16.36   $16.35   $16.40  
  7 purchase totals = $344.49       $373.9574   $373.97   $373.95   $374.00