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 $244.72   8.207%   $264.8042   $264.80   $264.80   $264.80  
  Purchase #2 $196.39   5.333%   $206.8635   $206.86   $206.85   $206.90  
  Purchase #3 $62.66   10.678%   $69.3508   $69.35   $69.35   $69.40  
  Purchase #4 $162.73   6.157%   $172.7493   $172.75   $172.75   $172.70  
  Purchase #5 $43.49   10.704%   $48.1452   $48.15   $48.15   $48.10  
  Purchase #6 $161.50   6.294%   $171.6648   $171.66   $171.65   $171.70  
  Purchase #7 $185.99   6.371%   $197.8394   $197.84   $197.85   $197.80  
  7 purchase totals = $1,057.48       $1,131.4172   $1,131.41   $1,131.40   $1,131.40