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 $28.86   12.632%   $32.5056   $32.51   $32.50   $32.50  
  Purchase #2 $88.26   8.847%   $96.0684   $96.07   $96.05   $96.10  
  Purchase #3 $106.61   11.798%   $119.1878   $119.19   $119.20   $119.20  
  Purchase #4 $141.78   10.503%   $156.6712   $156.67   $156.65   $156.70  
  Purchase #5 $19.94   5.212%   $20.9793   $20.98   $21.00   $21.00  
  Purchase #6 $205.54   6.866%   $219.6524   $219.65   $219.65   $219.70  
  Purchase #7 $105.86   9.666%   $116.0924   $116.09   $116.10   $116.10  
  7 purchase totals = $696.85       $761.1571   $761.16   $761.15   $761.30