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 $211.53   5.392%   $222.9357   $222.94   $222.95   $222.90  
  Purchase #2 $214.33   8.870%   $233.3411   $233.34   $233.35   $233.30  
  Purchase #3 $16.26   4.457%   $16.9847   $16.98   $17.00   $17.00  
  Purchase #4 $250.65   13.782%   $285.1946   $285.19   $285.20   $285.20  
  Purchase #5 $166.50   10.282%   $183.6195   $183.62   $183.60   $183.60  
  Purchase #6 $115.66   4.742%   $121.1446   $121.14   $121.15   $121.10  
  Purchase #7 $177.45   7.669%   $191.0586   $191.06   $191.05   $191.10  
  7 purchase totals = $1,152.38       $1,254.2788   $1,254.27   $1,254.30   $1,254.20