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 $231.77   11.242%   $257.8256   $257.83   $257.85   $257.80  
  Purchase #2 $6.41   8.129%   $6.9311   $6.93   $6.95   $6.90  
  Purchase #3 $86.58   7.177%   $92.7938   $92.79   $92.80   $92.80  
  Purchase #4 $247.80   3.174%   $255.6652   $255.67   $255.65   $255.70  
  Purchase #5 $62.87   5.271%   $66.1839   $66.18   $66.20   $66.20  
  Purchase #6 $106.29   4.316%   $110.8775   $110.88   $110.90   $110.90  
  Purchase #7 $212.84   9.392%   $232.8299   $232.83   $232.85   $232.80  
  7 purchase totals = $954.56       $1,023.1070   $1,023.11   $1,023.20   $1,023.10