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 $211.98   6.723%   $226.2314   $226.23   $226.25   $226.20  
  Purchase #2 $136.93   8.744%   $148.9032   $148.90   $148.90   $148.90  
  Purchase #3 $34.86   12.168%   $39.1018   $39.10   $39.10   $39.10  
  Purchase #4 $176.77   5.247%   $186.0451   $186.05   $186.05   $186.00  
  Purchase #5 $153.29   8.368%   $166.1173   $166.12   $166.10   $166.10  
  Purchase #6 $183.72   9.195%   $200.6131   $200.61   $200.60   $200.60  
  Purchase #7 $101.39   4.590%   $106.0438   $106.04   $106.05   $106.00  
  7 purchase totals = $998.94       $1,073.0557   $1,073.05   $1,073.05   $1,072.90