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 $207.96   12.524%   $234.0049   $234.00   $234.00   $234.00  
  Purchase #2 $136.56   11.766%   $152.6276   $152.63   $152.65   $152.60  
  Purchase #3 $68.56   9.255%   $74.9052   $74.91   $74.90   $74.90  
  Purchase #4 $242.35   11.524%   $270.2784   $270.28   $270.30   $270.30  
  Purchase #5 $64.48   9.647%   $70.7004   $70.70   $70.70   $70.70  
  Purchase #6 $66.73   5.667%   $70.5116   $70.51   $70.50   $70.50  
  Purchase #7 $198.95   11.229%   $221.2901   $221.29   $221.30   $221.30  
  7 purchase totals = $985.59       $1,094.3182   $1,094.32   $1,094.35   $1,094.30