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 $227.95   7.526%   $245.1055   $245.11   $245.10   $245.10  
  Purchase #2 $62.25   7.373%   $66.8397   $66.84   $66.85   $66.80  
  Purchase #3 $113.35   11.344%   $126.2084   $126.21   $126.20   $126.20  
  Purchase #4 $93.48   4.451%   $97.6408   $97.64   $97.65   $97.60  
  Purchase #5 $107.99   10.684%   $119.5277   $119.53   $119.55   $119.50  
  Purchase #6 $203.32   13.320%   $230.4022   $230.40   $230.40   $230.40  
  Purchase #7 $127.54   6.526%   $135.8633   $135.86   $135.85   $135.90  
  7 purchase totals = $935.88       $1,021.5876   $1,021.59   $1,021.60   $1,021.50