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 $41.85   6.433%   $44.5422   $44.54   $44.55   $44.50  
  Purchase #2 $95.64   11.581%   $106.7161   $106.72   $106.70   $106.70  
  Purchase #3 $92.81   4.283%   $96.7851   $96.79   $96.80   $96.80  
  Purchase #4 $71.68   9.481%   $78.476   $78.48   $78.50   $78.50  
  Purchase #5 $132.68   3.815%   $137.7417   $137.74   $137.75   $137.70  
  Purchase #6 $235.79   5.566%   $248.9141   $248.91   $248.90   $248.90  
  Purchase #7 $9.41   4.319%   $9.8164   $9.82   $9.80   $9.80  
  7 purchase totals = $679.86       $722.9916   $723.00   $723.00   $722.90