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 $152.80   8.329%   $165.5267   $165.53   $165.55   $165.50  
  Purchase #2 $69.96   4.253%   $72.9354   $72.94   $72.95   $72.90  
  Purchase #3 $234.40   11.282%   $260.845   $260.85   $260.85   $260.80  
  Purchase #4 $217.65   9.468%   $238.2571   $238.26   $238.25   $238.30  
  Purchase #5 $30.92   4.784%   $32.3992   $32.40   $32.40   $32.40  
  Purchase #6 $200.47   3.709%   $207.9054   $207.91   $207.90   $207.90  
  Purchase #7 $174.89   13.699%   $198.8482   $198.85   $198.85   $198.80  
  7 purchase totals = $1,081.09       $1,176.7170   $1,176.74   $1,176.75   $1,176.60