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 $161.98   3.816%   $168.1612   $168.16   $168.15   $168.20  
  Purchase #2 $218.96   11.232%   $243.5536   $243.55   $243.55   $243.60  
  Purchase #3 $184.28   11.109%   $204.7517   $204.75   $204.75   $204.80  
  Purchase #4 $81.83   12.346%   $91.9327   $91.93   $91.95   $91.90  
  Purchase #5 $211.42   6.869%   $225.9424   $225.94   $225.95   $225.90  
  Purchase #6 $136.71   5.601%   $144.3671   $144.37   $144.35   $144.40  
  Purchase #7 $152.44   3.198%   $157.315   $157.32   $157.30   $157.30  
  7 purchase totals = $1,147.62       $1,236.0237   $1,236.02   $1,236.00   $1,236.10