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 $22.61   8.811%   $24.6022   $24.60   $24.60   $24.60  
  Purchase #2 $214.53   6.425%   $228.3136   $228.31   $228.30   $228.30  
  Purchase #3 $69.94   13.670%   $79.5008   $79.50   $79.50   $79.50  
  Purchase #4 $204.87   13.123%   $231.7551   $231.76   $231.75   $231.80  
  Purchase #5 $150.89   11.404%   $168.0975   $168.10   $168.10   $168.10  
  Purchase #6 $46.89   8.484%   $50.8681   $50.87   $50.85   $50.90  
  Purchase #7 $244.45   11.362%   $272.2244   $272.22   $272.20   $272.20  
  7 purchase totals = $954.18       $1,055.3617   $1,055.36   $1,055.30   $1,055.40