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 $185.48   8.582%   $201.3979   $201.40   $201.40   $201.40  
  Purchase #2 $67.95   8.148%   $73.4866   $73.49   $73.50   $73.50  
  Purchase #3 $52.73   12.478%   $59.3096   $59.31   $59.30   $59.30  
  Purchase #4 $55.30   11.463%   $61.639   $61.64   $61.65   $61.60  
  Purchase #5 $245.37   12.103%   $275.0671   $275.07   $275.05   $275.10  
  Purchase #6 $124.61   9.531%   $136.4866   $136.49   $136.50   $136.50  
  Purchase #7 $72.26   6.855%   $77.2134   $77.21   $77.20   $77.20  
  7 purchase totals = $803.70       $884.6002   $884.61   $884.60   $884.60