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 $153.86   6.467%   $163.8101   $163.81   $163.80   $163.80  
  Purchase #2 $149.48   11.857%   $167.2038   $167.20   $167.20   $167.20  
  Purchase #3 $155.51   5.644%   $164.287   $164.29   $164.30   $164.30  
  Purchase #4 $64.46   13.154%   $72.9391   $72.94   $72.95   $72.90  
  Purchase #5 $65.28   6.648%   $69.6198   $69.62   $69.60   $69.60  
  Purchase #6 $85.50   8.134%   $92.4546   $92.45   $92.45   $92.50  
  Purchase #7 $206.60   3.580%   $213.9963   $214.00   $214.00   $214.00  
  7 purchase totals = $880.69       $944.3107   $944.31   $944.30   $944.30