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 $180.84   6.576%   $192.732   $192.73   $192.75   $192.70  
  Purchase #2 $170.51   9.866%   $187.3325   $187.33   $187.35   $187.30  
  Purchase #3 $39.86   8.767%   $43.3545   $43.35   $43.35   $43.40  
  Purchase #4 $246.71   4.290%   $257.2939   $257.29   $257.30   $257.30  
  Purchase #5 $226.61   5.434%   $238.924   $238.92   $238.90   $238.90  
  Purchase #6 $138.98   8.791%   $151.1977   $151.20   $151.20   $151.20  
  Purchase #7 $159.61   10.827%   $176.891   $176.89   $176.90   $176.90  
  7 purchase totals = $1,163.12       $1,247.7256   $1,247.71   $1,247.75   $1,247.70