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 $182.89   11.838%   $204.5405   $204.54   $204.55   $204.50  
  Purchase #2 $172.82   10.597%   $191.1337   $191.13   $191.15   $191.10  
  Purchase #3 $184.94   13.753%   $210.3748   $210.37   $210.35   $210.40  
  Purchase #4 $239.26   10.581%   $264.5761   $264.58   $264.60   $264.60  
  Purchase #5 $119.89   12.657%   $135.0645   $135.06   $135.05   $135.10  
  Purchase #6 $33.34   8.111%   $36.0442   $36.04   $36.05   $36.00  
  Purchase #7 $28.65   5.440%   $30.2086   $30.21   $30.20   $30.20  
  7 purchase totals = $961.79       $1,071.9424   $1,071.93   $1,071.95   $1,071.90