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 $82.34   3.185%   $84.9625   $84.96   $84.95   $85.00  
  Purchase #2 $111.32   10.139%   $122.6067   $122.61   $122.60   $122.60  
  Purchase #3 $233.69   13.683%   $265.6658   $265.67   $265.65   $265.70  
  Purchase #4 $64.50   7.474%   $69.3207   $69.32   $69.30   $69.30  
  Purchase #5 $181.80   11.121%   $202.018   $202.02   $202.00   $202.00  
  Purchase #6 $75.74   11.169%   $84.1994   $84.20   $84.20   $84.20  
  Purchase #7 $74.65   3.452%   $77.2269   $77.23   $77.25   $77.20  
  7 purchase totals = $824.04       $906.0000   $906.01   $905.95   $906.00