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 $113.33   4.849%   $118.8254   $118.83   $118.85   $118.80  
  Purchase #2 $57.73   11.546%   $64.3955   $64.40   $64.40   $64.40  
  Purchase #3 $125.41   9.618%   $137.4719   $137.47   $137.45   $137.50  
  Purchase #4 $226.47   4.664%   $237.0326   $237.03   $237.05   $237.00  
  Purchase #5 $179.76   13.454%   $203.9449   $203.94   $203.95   $203.90  
  Purchase #6 $223.69   9.472%   $244.8779   $244.88   $244.90   $244.90  
  Purchase #7 $156.32   8.783%   $170.0496   $170.05   $170.05   $170.00  
  7 purchase totals = $1,082.71       $1,176.5978   $1,176.60   $1,176.65   $1,176.50