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 $46.80   3.462%   $48.4202   $48.42   $48.40   $48.40  
  Purchase #2 $152.85   10.689%   $169.1881   $169.19   $169.20   $169.20  
  Purchase #3 $147.28   4.703%   $154.2066   $154.21   $154.20   $154.20  
  Purchase #4 $21.71   9.444%   $23.7603   $23.76   $23.75   $23.80  
  Purchase #5 $250.46   10.243%   $276.1146   $276.11   $276.10   $276.10  
  Purchase #6 $110.79   13.336%   $125.565   $125.57   $125.55   $125.60  
  Purchase #7 $219.53   3.373%   $226.9347   $226.93   $226.95   $226.90  
  7 purchase totals = $949.42       $1,024.1895   $1,024.19   $1,024.15   $1,024.20