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 $104.73   8.781%   $113.9263   $113.93   $113.95   $113.90  
  Purchase #2 $142.93   6.616%   $152.3862   $152.39   $152.40   $152.40  
  Purchase #3 $146.36   5.290%   $154.1024   $154.10   $154.10   $154.10  
  Purchase #4 $93.48   7.484%   $100.476   $100.48   $100.50   $100.50  
  Purchase #5 $221.63   8.469%   $240.3998   $240.40   $240.40   $240.40  
  Purchase #6 $118.47   5.560%   $125.0569   $125.06   $125.05   $125.10  
  Purchase #7 $237.32   9.837%   $260.6652   $260.67   $260.65   $260.70  
  7 purchase totals = $1,064.92       $1,147.0128   $1,147.03   $1,147.05   $1,147.10