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 $246.40   9.189%   $269.0417   $269.04   $269.05   $269.00  
  Purchase #2 $56.77   8.579%   $61.6403   $61.64   $61.65   $61.60  
  Purchase #3 $219.58   11.223%   $244.2235   $244.22   $244.20   $244.20  
  Purchase #4 $136.73   10.286%   $150.794   $150.79   $150.80   $150.80  
  Purchase #5 $195.61   3.681%   $202.8104   $202.81   $202.80   $202.80  
  Purchase #6 $63.63   9.779%   $69.8524   $69.85   $69.85   $69.90  
  Purchase #7 $191.73   10.645%   $212.1397   $212.14   $212.15   $212.10  
  7 purchase totals = $1,110.45       $1,210.5020   $1,210.49   $1,210.50   $1,210.40