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 $246.86   7.250%   $264.7574   $264.76   $264.75   $264.80  
  Purchase #2 $26.55   11.767%   $29.6741   $29.67   $29.65   $29.70  
  Purchase #3 $50.85   9.132%   $55.4936   $55.49   $55.50   $55.50  
  Purchase #4 $76.62   9.431%   $83.846   $83.85   $83.85   $83.80  
  Purchase #5 $164.29   13.865%   $187.0688   $187.07   $187.05   $187.10  
  Purchase #6 $107.71   4.102%   $112.1283   $112.13   $112.15   $112.10  
  Purchase #7 $106.92   5.695%   $113.0091   $113.01   $113.00   $113.00  
  7 purchase totals = $779.80       $845.9773   $845.98   $845.95   $846.00