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 $88.82   11.177%   $98.7474   $98.75   $98.75   $98.70  
  Purchase #2 $14.55   5.763%   $15.3885   $15.39   $15.40   $15.40  
  Purchase #3 $96.95   3.494%   $100.3374   $100.34   $100.35   $100.30  
  Purchase #4 $192.50   13.814%   $219.092   $219.09   $219.10   $219.10  
  Purchase #5 $141.64   11.692%   $158.2005   $158.20   $158.20   $158.20  
  Purchase #6 $155.30   8.792%   $168.954   $168.95   $168.95   $169.00  
  Purchase #7 $238.42   5.666%   $251.9289   $251.93   $251.95   $251.90  
  7 purchase totals = $928.18       $1,012.6487   $1,012.65   $1,012.70   $1,012.60