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 $58.49   4.820%   $61.3092   $61.31   $61.30   $61.30  
  Purchase #2 $66.65   6.138%   $70.741   $70.74   $70.75   $70.70  
  Purchase #3 $116.82   12.299%   $131.1877   $131.19   $131.20   $131.20  
  Purchase #4 $75.64   7.418%   $81.251   $81.25   $81.25   $81.30  
  Purchase #5 $150.30   3.565%   $155.6582   $155.66   $155.65   $155.70  
  Purchase #6 $238.42   6.670%   $254.3226   $254.32   $254.30   $254.30  
  Purchase #7 $66.84   7.708%   $71.992   $71.99   $72.00   $72.00  
  7 purchase totals = $773.16       $826.4617   $826.46   $826.45   $826.50