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 $241.98   4.614%   $253.145   $253.15   $253.15   $253.10  
  Purchase #2 $86.37   8.521%   $93.7296   $93.73   $93.75   $93.70  
  Purchase #3 $53.28   5.113%   $56.0042   $56.00   $56.00   $56.00  
  Purchase #4 $183.51   5.694%   $193.9591   $193.96   $193.95   $194.00  
  Purchase #5 $167.26   6.777%   $178.5952   $178.60   $178.60   $178.60  
  Purchase #6 $99.84   8.360%   $108.1866   $108.19   $108.20   $108.20  
  Purchase #7 $76.28   10.592%   $84.3596   $84.36   $84.35   $84.40  
  7 purchase totals = $908.52       $967.9793   $967.99   $968.00   $968.00