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 $108.87   12.282%   $122.2414   $122.24   $122.25   $122.20  
  Purchase #2 $250.32   9.592%   $274.3307   $274.33   $274.35   $274.30  
  Purchase #3 $88.76   13.603%   $100.834   $100.83   $100.85   $100.80  
  Purchase #4 $215.67   13.145%   $244.0198   $244.02   $244.00   $244.00  
  Purchase #5 $88.79   6.564%   $94.6182   $94.62   $94.60   $94.60  
  Purchase #6 $231.67   11.540%   $258.4047   $258.40   $258.40   $258.40  
  Purchase #7 $173.28   10.871%   $192.1173   $192.12   $192.10   $192.10  
  7 purchase totals = $1,157.36       $1,286.5661   $1,286.56   $1,286.55   $1,286.40