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 $85.94   12.652%   $96.8131   $96.81   $96.80   $96.80  
  Purchase #2 $148.57   9.697%   $162.9768   $162.98   $163.00   $163.00  
  Purchase #3 $15.65   3.397%   $16.1816   $16.18   $16.20   $16.20  
  Purchase #4 $190.67   6.799%   $203.6337   $203.63   $203.65   $203.60  
  Purchase #5 $101.88   11.375%   $113.4689   $113.47   $113.45   $113.50  
  Purchase #6 $223.95   7.580%   $240.9254   $240.93   $240.95   $240.90  
  Purchase #7 $130.65   9.484%   $143.0408   $143.04   $143.05   $143.00  
  7 purchase totals = $897.31       $977.0403   $977.04   $977.10   $977.00