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 $60.68   6.201%   $64.4428   $64.44   $64.45   $64.40  
  Purchase #2 $213.31   8.436%   $231.3048   $231.30   $231.30   $231.30  
  Purchase #3 $45.58   5.514%   $48.0933   $48.09   $48.10   $48.10  
  Purchase #4 $242.50   5.138%   $254.9597   $254.96   $254.95   $255.00  
  Purchase #5 $12.52   4.646%   $13.1017   $13.10   $13.10   $13.10  
  Purchase #6 $92.67   3.555%   $95.9644   $95.96   $95.95   $96.00  
  Purchase #7 $220.92   3.693%   $229.0786   $229.08   $229.10   $229.10  
  7 purchase totals = $888.18       $936.9453   $936.93   $936.95   $937.00