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 $238.48   7.658%   $256.7428   $256.74   $256.75   $256.70  
  Purchase #2 $114.97   8.593%   $124.8494   $124.85   $124.85   $124.80  
  Purchase #3 $215.71   6.161%   $228.9999   $229.00   $229.00   $229.00  
  Purchase #4 $139.79   10.160%   $153.9927   $153.99   $154.00   $154.00  
  Purchase #5 $13.78   6.347%   $14.6546   $14.65   $14.65   $14.70  
  Purchase #6 $71.95   11.830%   $80.4617   $80.46   $80.45   $80.50  
  Purchase #7 $153.66   7.555%   $165.269   $165.27   $165.25   $165.30  
  7 purchase totals = $948.34       $1,024.9701   $1,024.96   $1,024.95   $1,025.00