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 $146.98   10.218%   $161.9984   $162.00   $162.00   $162.00  
  Purchase #2 $193.93   9.758%   $212.8537   $212.85   $212.85   $212.90  
  Purchase #3 $95.96   6.149%   $101.8606   $101.86   $101.85   $101.90  
  Purchase #4 $33.76   7.856%   $36.4122   $36.41   $36.40   $36.40  
  Purchase #5 $71.86   3.874%   $74.6439   $74.64   $74.65   $74.60  
  Purchase #6 $179.36   8.427%   $194.4747   $194.47   $194.45   $194.50  
  Purchase #7 $141.51   7.497%   $152.119   $152.12   $152.10   $152.10  
  7 purchase totals = $863.36       $934.3625   $934.35   $934.30   $934.40