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 $57.49   12.757%   $64.824   $64.82   $64.80   $64.80  
  Purchase #2 $148.28   5.742%   $156.7942   $156.79   $156.80   $156.80  
  Purchase #3 $111.83   10.146%   $123.1763   $123.18   $123.20   $123.20  
  Purchase #4 $163.70   10.322%   $180.5971   $180.60   $180.60   $180.60  
  Purchase #5 $162.44   9.537%   $177.9319   $177.93   $177.95   $177.90  
  Purchase #6 $180.54   8.333%   $195.5844   $195.58   $195.60   $195.60  
  Purchase #7 $196.93   3.843%   $204.498   $204.50   $204.50   $204.50  
  7 purchase totals = $1,021.21       $1,103.4059   $1,103.40   $1,103.45   $1,103.40