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 $180.82   8.343%   $195.9058   $195.91   $195.90   $195.90  
  Purchase #2 $152.94   3.206%   $157.8433   $157.84   $157.85   $157.80  
  Purchase #3 $232.42   11.318%   $258.7253   $258.73   $258.75   $258.70  
  Purchase #4 $183.89   12.119%   $206.1756   $206.18   $206.20   $206.20  
  Purchase #5 $19.77   8.390%   $21.4287   $21.43   $21.45   $21.40  
  Purchase #6 $59.30   4.591%   $62.0225   $62.02   $62.00   $62.00  
  Purchase #7 $98.89   13.636%   $112.3746   $112.37   $112.35   $112.40  
  7 purchase totals = $928.03       $1,014.4758   $1,014.48   $1,014.50   $1,014.40