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 $16.85   12.843%   $19.014   $19.01   $19.00   $19.00  
  Purchase #2 $92.76   13.546%   $105.3253   $105.33   $105.35   $105.30  
  Purchase #3 $87.73   10.104%   $96.5942   $96.59   $96.60   $96.60  
  Purchase #4 $190.62   5.858%   $201.7865   $201.79   $201.80   $201.80  
  Purchase #5 $69.46   3.723%   $72.046   $72.05   $72.05   $72.00  
  Purchase #6 $35.73   5.480%   $37.688   $37.69   $37.70   $37.70  
  Purchase #7 $23.66   9.291%   $25.8583   $25.86   $25.85   $25.90  
  7 purchase totals = $516.81       $558.3123   $558.32   $558.35   $558.30