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 $58.25   4.253%   $60.7274   $60.73   $60.75   $60.70  
  Purchase #2 $224.98   9.550%   $246.4656   $246.47   $246.45   $246.50  
  Purchase #3 $124.93   9.766%   $137.1307   $137.13   $137.15   $137.10  
  Purchase #4 $157.83   4.200%   $164.4589   $164.46   $164.45   $164.50  
  Purchase #5 $26.35   5.655%   $27.8401   $27.84   $27.85   $27.80  
  Purchase #6 $117.46   13.835%   $133.7106   $133.71   $133.70   $133.70  
  Purchase #7 $75.43   7.535%   $81.1137   $81.11   $81.10   $81.10  
  7 purchase totals = $785.23       $851.4470   $851.45   $851.45   $851.40