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 $217.46   11.715%   $242.9354   $242.94   $242.95   $242.90  
  Purchase #2 $43.83   13.123%   $49.5818   $49.58   $49.60   $49.60  
  Purchase #3 $159.95   11.801%   $178.8257   $178.83   $178.85   $178.80  
  Purchase #4 $107.89   6.801%   $115.2276   $115.23   $115.25   $115.20  
  Purchase #5 $201.96   12.570%   $227.3464   $227.35   $227.35   $227.30  
  Purchase #6 $65.61   9.657%   $71.946   $71.95   $71.95   $71.90  
  Purchase #7 $78.30   3.763%   $81.2464   $81.25   $81.25   $81.20  
  7 purchase totals = $875.00       $967.1093   $967.13   $967.20   $966.90