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 $229.91   10.526%   $254.1103   $254.11   $254.10   $254.10  
  Purchase #2 $118.41   7.419%   $127.1948   $127.19   $127.20   $127.20  
  Purchase #3 $75.88   12.495%   $85.3612   $85.36   $85.35   $85.40  
  Purchase #4 $213.31   11.561%   $237.9708   $237.97   $237.95   $238.00  
  Purchase #5 $236.80   3.261%   $244.522   $244.52   $244.50   $244.50  
  Purchase #6 $112.48   4.560%   $117.6091   $117.61   $117.60   $117.60  
  Purchase #7 $29.39   4.807%   $30.8028   $30.80   $30.80   $30.80  
  7 purchase totals = $1,016.18       $1,097.5710   $1,097.56   $1,097.50   $1,097.60