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 $136.46   11.273%   $151.8431   $151.84   $151.85   $151.80  
  Purchase #2 $32.97   9.186%   $35.9986   $36.00   $36.00   $36.00  
  Purchase #3 $53.25   3.670%   $55.2043   $55.20   $55.20   $55.20  
  Purchase #4 $153.34   7.563%   $164.9371   $164.94   $164.95   $164.90  
  Purchase #5 $94.46   8.229%   $102.2331   $102.23   $102.25   $102.20  
  Purchase #6 $211.86   6.545%   $225.7262   $225.73   $225.75   $225.70  
  Purchase #7 $191.79   12.644%   $216.0399   $216.04   $216.05   $216.00  
  7 purchase totals = $874.13       $951.9823   $951.98   $952.05   $951.80