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 $232.56   10.817%   $257.716   $257.72   $257.70   $257.70  
  Purchase #2 $225.98   11.147%   $251.17   $251.17   $251.15   $251.20  
  Purchase #3 $110.84   11.806%   $123.9258   $123.93   $123.95   $123.90  
  Purchase #4 $192.27   8.874%   $209.332   $209.33   $209.35   $209.30  
  Purchase #5 $192.54   8.839%   $209.5586   $209.56   $209.55   $209.60  
  Purchase #6 $6.51   9.525%   $7.1301   $7.13   $7.15   $7.10  
  Purchase #7 $146.77   13.271%   $166.2478   $166.25   $166.25   $166.20  
  7 purchase totals = $1,107.47       $1,225.0803   $1,225.09   $1,225.10   $1,225.00