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 $211.56   11.439%   $235.7603   $235.76   $235.75   $235.80  
  Purchase #2 $75.41   9.541%   $82.6049   $82.60   $82.60   $82.60  
  Purchase #3 $38.91   13.516%   $44.1691   $44.17   $44.15   $44.20  
  Purchase #4 $111.91   6.204%   $118.8529   $118.85   $118.85   $118.90  
  Purchase #5 $220.71   6.205%   $234.4051   $234.41   $234.40   $234.40  
  Purchase #6 $23.56   7.322%   $25.2851   $25.29   $25.30   $25.30  
  Purchase #7 $108.46   11.871%   $121.3353   $121.34   $121.35   $121.30  
  7 purchase totals = $790.52       $862.4127   $862.42   $862.40   $862.50