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 $58.74   11.751%   $65.6425   $65.64   $65.65   $65.60  
  Purchase #2 $202.86   7.707%   $218.4944   $218.49   $218.50   $218.50  
  Purchase #3 $25.93   4.844%   $27.186   $27.19   $27.20   $27.20  
  Purchase #4 $233.67   5.103%   $245.5942   $245.59   $245.60   $245.60  
  Purchase #5 $250.94   3.616%   $260.014   $260.01   $260.00   $260.00  
  Purchase #6 $19.90   6.543%   $21.2021   $21.20   $21.20   $21.20  
  Purchase #7 $10.65   11.373%   $11.8612   $11.86   $11.85   $11.90  
  7 purchase totals = $802.69       $849.9944   $849.98   $850.00   $850.00