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 $201.85   13.285%   $228.6658   $228.67   $228.65   $228.70  
  Purchase #2 $65.91   10.716%   $72.9729   $72.97   $72.95   $73.00  
  Purchase #3 $91.84   13.240%   $103.9996   $104.00   $104.00   $104.00  
  Purchase #4 $50.91   6.223%   $54.0781   $54.08   $54.10   $54.10  
  Purchase #5 $182.25   12.825%   $205.6236   $205.62   $205.60   $205.60  
  Purchase #6 $107.40   3.630%   $111.2986   $111.30   $111.30   $111.30  
  Purchase #7 $187.42   11.303%   $208.6041   $208.60   $208.60   $208.60  
  7 purchase totals = $887.58       $985.2427   $985.24   $985.20   $985.30