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 $172.84   13.259%   $195.7569   $195.76   $195.75   $195.80  
  Purchase #2 $105.29   12.473%   $118.4228   $118.42   $118.40   $118.40  
  Purchase #3 $208.62   11.347%   $232.2921   $232.29   $232.30   $232.30  
  Purchase #4 $218.84   8.121%   $236.612   $236.61   $236.60   $236.60  
  Purchase #5 $157.77   12.298%   $177.1726   $177.17   $177.15   $177.20  
  Purchase #6 $56.30   6.722%   $60.0845   $60.08   $60.10   $60.10  
  Purchase #7 $95.76   8.221%   $103.6324   $103.63   $103.65   $103.60  
  7 purchase totals = $1,015.42       $1,123.9733   $1,123.96   $1,123.95   $1,124.00