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 $241.75   3.414%   $250.0033   $250.00   $250.00   $250.00  
  Purchase #2 $103.74   12.632%   $116.8444   $116.84   $116.85   $116.80  
  Purchase #3 $235.50   11.143%   $261.7418   $261.74   $261.75   $261.70  
  Purchase #4 $59.45   4.317%   $62.0165   $62.02   $62.00   $62.00  
  Purchase #5 $138.34   12.295%   $155.3489   $155.35   $155.35   $155.30  
  Purchase #6 $210.64   4.426%   $219.9629   $219.96   $219.95   $220.00  
  Purchase #7 $154.80   13.602%   $175.8559   $175.86   $175.85   $175.90  
  7 purchase totals = $1,144.22       $1,241.7737   $1,241.77   $1,241.75   $1,241.70