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 $56.68   4.237%   $59.0815   $59.08   $59.10   $59.10  
  Purchase #2 $126.41   11.384%   $140.8005   $140.80   $140.80   $140.80  
  Purchase #3 $50.98   6.694%   $54.3926   $54.39   $54.40   $54.40  
  Purchase #4 $214.42   13.232%   $242.7921   $242.79   $242.80   $242.80  
  Purchase #5 $11.44   4.407%   $11.9442   $11.94   $11.95   $11.90  
  Purchase #6 $86.38   11.132%   $95.9958   $96.00   $96.00   $96.00  
  Purchase #7 $151.63   12.818%   $171.0659   $171.07   $171.05   $171.10  
  7 purchase totals = $697.94       $776.0726   $776.07   $776.10   $776.10