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 $59.43   4.297%   $61.9837   $61.98   $62.00   $62.00  
  Purchase #2 $70.46   13.650%   $80.0778   $80.08   $80.10   $80.10  
  Purchase #3 $47.44   13.753%   $53.9644   $53.96   $53.95   $54.00  
  Purchase #4 $182.55   13.691%   $207.5429   $207.54   $207.55   $207.50  
  Purchase #5 $213.40   12.474%   $240.0195   $240.02   $240.00   $240.00  
  Purchase #6 $217.42   10.108%   $239.3968   $239.40   $239.40   $239.40  
  Purchase #7 $74.84   9.521%   $81.9655   $81.97   $81.95   $82.00  
  7 purchase totals = $865.54       $964.9506   $964.95   $964.95   $965.00