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 $30.69   12.155%   $34.4204   $34.42   $34.40   $34.40  
  Purchase #2 $56.87   11.473%   $63.3947   $63.39   $63.40   $63.40  
  Purchase #3 $24.29   13.202%   $27.4968   $27.50   $27.50   $27.50  
  Purchase #4 $111.55   8.851%   $121.4233   $121.42   $121.40   $121.40  
  Purchase #5 $128.71   5.431%   $135.7002   $135.70   $135.70   $135.70  
  Purchase #6 $111.70   10.367%   $123.2799   $123.28   $123.30   $123.30  
  Purchase #7 $241.92   5.349%   $254.8603   $254.86   $254.85   $254.90  
  7 purchase totals = $705.73       $760.5756   $760.57   $760.55   $760.60