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 $46.92   6.644%   $50.0374   $50.04   $50.05   $50.00  
  Purchase #2 $176.40   9.257%   $192.7293   $192.73   $192.75   $192.70  
  Purchase #3 $164.87   7.643%   $177.471   $177.47   $177.45   $177.50  
  Purchase #4 $197.98   10.765%   $219.2925   $219.29   $219.30   $219.30  
  Purchase #5 $203.90   6.347%   $216.8415   $216.84   $216.85   $216.80  
  Purchase #6 $74.54   4.310%   $77.7527   $77.75   $77.75   $77.80  
  Purchase #7 $23.89   7.139%   $25.5955   $25.60   $25.60   $25.60  
  7 purchase totals = $888.50       $959.7199   $959.72   $959.75   $959.70