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 $57.64   4.484%   $60.2246   $60.22   $60.20   $60.20  
  Purchase #2 $164.52   3.764%   $170.7125   $170.71   $170.70   $170.70  
  Purchase #3 $221.43   7.706%   $238.4934   $238.49   $238.50   $238.50  
  Purchase #4 $95.75   3.227%   $98.8399   $98.84   $98.85   $98.80  
  Purchase #5 $58.65   11.188%   $65.2118   $65.21   $65.20   $65.20  
  Purchase #6 $223.95   7.828%   $241.4808   $241.48   $241.50   $241.50  
  Purchase #7 $182.68   6.352%   $194.2838   $194.28   $194.30   $194.30  
  7 purchase totals = $1,004.62       $1,069.2468   $1,069.23   $1,069.25   $1,069.20