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 $244.89   6.285%   $260.2813   $260.28   $260.30   $260.30  
  Purchase #2 $134.36   13.522%   $152.5282   $152.53   $152.55   $152.50  
  Purchase #3 $142.60   13.413%   $161.7269   $161.73   $161.75   $161.70  
  Purchase #4 $153.73   12.414%   $172.814   $172.81   $172.80   $172.80  
  Purchase #5 $232.42   5.525%   $245.2612   $245.26   $245.25   $245.30  
  Purchase #6 $94.99   9.312%   $103.8355   $103.84   $103.85   $103.80  
  Purchase #7 $123.42   6.780%   $131.7879   $131.79   $131.80   $131.80  
  7 purchase totals = $1,126.41       $1,228.2350   $1,228.24   $1,228.30   $1,228.20