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 $180.93   11.286%   $201.3498   $201.35   $201.35   $201.30  
  Purchase #2 $29.80   8.417%   $32.3083   $32.31   $32.30   $32.30  
  Purchase #3 $232.74   10.348%   $256.8239   $256.82   $256.80   $256.80  
  Purchase #4 $124.39   6.435%   $132.3945   $132.39   $132.40   $132.40  
  Purchase #5 $207.71   12.589%   $233.8586   $233.86   $233.85   $233.90  
  Purchase #6 $39.43   4.758%   $41.3061   $41.31   $41.30   $41.30  
  Purchase #7 $131.71   11.459%   $146.8026   $146.80   $146.80   $146.80  
  7 purchase totals = $946.71       $1,044.8438   $1,044.84   $1,044.80   $1,044.80