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 $195.98   5.778%   $207.3037   $207.30   $207.30   $207.30  
  Purchase #2 $131.64   8.517%   $142.8518   $142.85   $142.85   $142.90  
  Purchase #3 $83.37   10.531%   $92.1497   $92.15   $92.15   $92.10  
  Purchase #4 $232.65   9.271%   $254.219   $254.22   $254.20   $254.20  
  Purchase #5 $246.64   5.699%   $260.696   $260.70   $260.70   $260.70  
  Purchase #6 $160.69   11.554%   $179.2561   $179.26   $179.25   $179.30  
  Purchase #7 $8.38   11.425%   $9.3374   $9.34   $9.35   $9.30  
  7 purchase totals = $1,059.35       $1,145.8137   $1,145.82   $1,145.80   $1,145.80