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 $84.98   13.277%   $96.2628   $96.26   $96.25   $96.30  
  Purchase #2 $110.30   5.289%   $116.1338   $116.13   $116.15   $116.10  
  Purchase #3 $68.65   6.342%   $73.0038   $73.00   $73.00   $73.00  
  Purchase #4 $97.62   11.351%   $108.7008   $108.70   $108.70   $108.70  
  Purchase #5 $40.53   11.458%   $45.1739   $45.17   $45.15   $45.20  
  Purchase #6 $218.74   12.623%   $246.3516   $246.35   $246.35   $246.40  
  Purchase #7 $147.51   7.551%   $158.6485   $158.65   $158.65   $158.60  
  7 purchase totals = $768.33       $844.2752   $844.26   $844.25   $844.30