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 $76.66   12.424%   $86.1842   $86.18   $86.20   $86.20  
  Purchase #2 $107.43   12.841%   $121.2251   $121.23   $121.25   $121.20  
  Purchase #3 $191.36   6.723%   $204.2251   $204.23   $204.25   $204.20  
  Purchase #4 $128.92   9.391%   $141.0269   $141.03   $141.05   $141.00  
  Purchase #5 $83.57   11.398%   $93.0953   $93.10   $93.10   $93.10  
  Purchase #6 $197.50   5.259%   $207.8865   $207.89   $207.90   $207.90  
  Purchase #7 $148.71   8.290%   $161.0381   $161.04   $161.05   $161.00  
  7 purchase totals = $934.15       $1,014.6812   $1,014.70   $1,014.80   $1,014.60