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 $63.50   10.795%   $70.3548   $70.35   $70.35   $70.40  
  Purchase #2 $112.95   6.129%   $119.8727   $119.87   $119.85   $119.90  
  Purchase #3 $84.56   4.614%   $88.4616   $88.46   $88.45   $88.50  
  Purchase #4 $228.52   8.684%   $248.3647   $248.36   $248.35   $248.40  
  Purchase #5 $238.26   12.759%   $268.6596   $268.66   $268.65   $268.70  
  Purchase #6 $122.89   10.766%   $136.1203   $136.12   $136.10   $136.10  
  Purchase #7 $243.82   8.141%   $263.6694   $263.67   $263.65   $263.70  
  7 purchase totals = $1,094.50       $1,195.5031   $1,195.49   $1,195.40   $1,195.70