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 $31.47   9.723%   $34.5298   $34.53   $34.55   $34.50  
  Purchase #2 $111.48   10.595%   $123.2913   $123.29   $123.30   $123.30  
  Purchase #3 $46.91   4.207%   $48.8835   $48.88   $48.90   $48.90  
  Purchase #4 $54.89   9.785%   $60.261   $60.26   $60.25   $60.30  
  Purchase #5 $57.40   9.480%   $62.8415   $62.84   $62.85   $62.80  
  Purchase #6 $216.67   3.529%   $224.3163   $224.32   $224.30   $224.30  
  Purchase #7 $232.35   4.469%   $242.7337   $242.73   $242.75   $242.70  
  7 purchase totals = $751.17       $796.8571   $796.85   $796.90   $796.80