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 $201.91   8.810%   $219.6983   $219.70   $219.70   $219.70  
  Purchase #2 $213.51   7.657%   $229.8585   $229.86   $229.85   $229.90  
  Purchase #3 $48.71   8.733%   $52.9638   $52.96   $52.95   $53.00  
  Purchase #4 $191.96   9.162%   $209.5474   $209.55   $209.55   $209.50  
  Purchase #5 $208.72   6.306%   $221.8819   $221.88   $221.90   $221.90  
  Purchase #6 $44.95   4.526%   $46.9844   $46.98   $47.00   $47.00  
  Purchase #7 $30.39   11.594%   $33.9134   $33.91   $33.90   $33.90  
  7 purchase totals = $940.15       $1,014.8477   $1,014.84   $1,014.85   $1,014.90