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 $77.41   6.207%   $82.2148   $82.21   $82.20   $82.20  
  Purchase #2 $6.63   8.592%   $7.1996   $7.20   $7.20   $7.20  
  Purchase #3 $56.35   5.768%   $59.6003   $59.60   $59.60   $59.60  
  Purchase #4 $84.92   12.162%   $95.248   $95.25   $95.25   $95.20  
  Purchase #5 $235.55   3.278%   $243.2713   $243.27   $243.25   $243.30  
  Purchase #6 $182.67   6.486%   $194.518   $194.52   $194.50   $194.50  
  Purchase #7 $117.40   5.640%   $124.0214   $124.02   $124.00   $124.00  
  7 purchase totals = $760.93       $806.0734   $806.07   $806.00   $806.00