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 $169.37   13.457%   $192.1621   $192.16   $192.15   $192.20  
  Purchase #2 $175.54   11.828%   $196.3029   $196.30   $196.30   $196.30  
  Purchase #3 $18.56   13.234%   $21.0162   $21.02   $21.00   $21.00  
  Purchase #4 $41.52   9.107%   $45.3012   $45.30   $45.30   $45.30  
  Purchase #5 $247.56   4.667%   $259.1136   $259.11   $259.10   $259.10  
  Purchase #6 $63.73   8.646%   $69.2401   $69.24   $69.25   $69.20  
  Purchase #7 $208.95   10.544%   $230.9817   $230.98   $231.00   $231.00  
  7 purchase totals = $925.23       $1,014.1178   $1,014.11   $1,014.10   $1,014.10