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 $169.26   12.154%   $189.8319   $189.83   $189.85   $189.80  
  Purchase #2 $200.66   8.509%   $217.7342   $217.73   $217.75   $217.70  
  Purchase #3 $188.64   3.411%   $195.0745   $195.07   $195.05   $195.10  
  Purchase #4 $51.81   5.142%   $54.4741   $54.47   $54.45   $54.50  
  Purchase #5 $80.34   9.373%   $87.8703   $87.87   $87.85   $87.90  
  Purchase #6 $209.50   6.149%   $222.3822   $222.38   $222.40   $222.40  
  Purchase #7 $114.61   7.283%   $122.957   $122.96   $122.95   $123.00  
  7 purchase totals = $1,014.82       $1,090.3242   $1,090.31   $1,090.30   $1,090.40