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 $201.98   12.217%   $226.6559   $226.66   $226.65   $226.70  
  Purchase #2 $10.89   13.714%   $12.3835   $12.38   $12.40   $12.40  
  Purchase #3 $144.80   8.687%   $157.3788   $157.38   $157.40   $157.40  
  Purchase #4 $186.42   10.636%   $206.2476   $206.25   $206.25   $206.20  
  Purchase #5 $116.66   8.167%   $126.1876   $126.19   $126.20   $126.20  
  Purchase #6 $99.80   6.847%   $106.6333   $106.63   $106.65   $106.60  
  Purchase #7 $176.89   13.540%   $200.8409   $200.84   $200.85   $200.80  
  7 purchase totals = $937.44       $1,036.3276   $1,036.33   $1,036.40   $1,036.30