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 $165.41   13.297%   $187.4046   $187.40   $187.40   $187.40  
  Purchase #2 $204.75   11.293%   $227.8724   $227.87   $227.85   $227.90  
  Purchase #3 $25.45   9.638%   $27.9029   $27.90   $27.90   $27.90  
  Purchase #4 $247.41   6.638%   $263.8331   $263.83   $263.85   $263.80  
  Purchase #5 $246.90   5.633%   $260.8079   $260.81   $260.80   $260.80  
  Purchase #6 $143.62   10.840%   $159.1884   $159.19   $159.20   $159.20  
  Purchase #7 $212.43   10.289%   $234.2869   $234.29   $234.30   $234.30  
  7 purchase totals = $1,245.97       $1,361.2962   $1,361.29   $1,361.30   $1,361.30