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 $230.61   5.790%   $243.9623   $243.96   $243.95   $244.00  
  Purchase #2 $57.64   11.834%   $64.4611   $64.46   $64.45   $64.50  
  Purchase #3 $168.64   3.221%   $174.0719   $174.07   $174.05   $174.10  
  Purchase #4 $92.31   7.833%   $99.5406   $99.54   $99.55   $99.50  
  Purchase #5 $163.96   12.389%   $184.273   $184.27   $184.25   $184.30  
  Purchase #6 $61.71   5.214%   $64.9276   $64.93   $64.95   $64.90  
  Purchase #7 $189.52   7.757%   $204.2211   $204.22   $204.20   $204.20  
  7 purchase totals = $964.39       $1,035.4576   $1,035.45   $1,035.40   $1,035.50