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 $53.79   10.565%   $59.4729   $59.47   $59.45   $59.50  
  Purchase #2 $64.36   7.291%   $69.0525   $69.05   $69.05   $69.10  
  Purchase #3 $27.89   6.791%   $29.784   $29.78   $29.80   $29.80  
  Purchase #4 $19.34   7.245%   $20.7412   $20.74   $20.75   $20.70  
  Purchase #5 $83.79   11.867%   $93.7334   $93.73   $93.75   $93.70  
  Purchase #6 $216.44   10.436%   $239.0277   $239.03   $239.05   $239.00  
  Purchase #7 $221.72   10.283%   $244.5195   $244.52   $244.50   $244.50  
  7 purchase totals = $687.33       $756.3312   $756.32   $756.35   $756.30