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 $32.27   13.614%   $36.6632   $36.66   $36.65   $36.70  
  Purchase #2 $177.45   10.259%   $195.6546   $195.65   $195.65   $195.70  
  Purchase #3 $195.99   4.394%   $204.6018   $204.60   $204.60   $204.60  
  Purchase #4 $135.54   3.856%   $140.7664   $140.77   $140.75   $140.80  
  Purchase #5 $46.58   11.850%   $52.0997   $52.10   $52.10   $52.10  
  Purchase #6 $190.41   4.554%   $199.0813   $199.08   $199.10   $199.10  
  Purchase #7 $46.42   12.670%   $52.3014   $52.30   $52.30   $52.30  
  7 purchase totals = $824.66       $881.1684   $881.16   $881.15   $881.30