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 $184.98   6.391%   $196.8021   $196.80   $196.80   $196.80  
  Purchase #2 $229.34   9.528%   $251.1915   $251.19   $251.20   $251.20  
  Purchase #3 $31.96   10.717%   $35.3852   $35.39   $35.40   $35.40  
  Purchase #4 $236.38   13.188%   $267.5538   $267.55   $267.55   $267.60  
  Purchase #5 $195.33   12.677%   $220.092   $220.09   $220.10   $220.10  
  Purchase #6 $53.49   4.526%   $55.911   $55.91   $55.90   $55.90  
  Purchase #7 $27.33   10.404%   $30.1734   $30.17   $30.15   $30.20  
  7 purchase totals = $958.81       $1,057.1090   $1,057.10   $1,057.10   $1,057.20