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 $56.95   5.675%   $60.1819   $60.18   $60.20   $60.20  
  Purchase #2 $81.79   13.675%   $92.9748   $92.97   $92.95   $93.00  
  Purchase #3 $100.49   3.701%   $104.2091   $104.21   $104.20   $104.20  
  Purchase #4 $204.87   7.665%   $220.5733   $220.57   $220.55   $220.60  
  Purchase #5 $236.52   4.560%   $247.3053   $247.31   $247.30   $247.30  
  Purchase #6 $28.87   4.281%   $30.1059   $30.11   $30.10   $30.10  
  Purchase #7 $250.47   8.182%   $270.9635   $270.96   $270.95   $271.00  
  7 purchase totals = $959.96       $1,026.3138   $1,026.31   $1,026.25   $1,026.40