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 $32.83   5.648%   $34.6842   $34.68   $34.70   $34.70  
  Purchase #2 $111.99   5.497%   $118.1461   $118.15   $118.15   $118.10  
  Purchase #3 $213.35   10.378%   $235.4915   $235.49   $235.50   $235.50  
  Purchase #4 $71.81   4.559%   $75.0838   $75.08   $75.10   $75.10  
  Purchase #5 $246.72   10.816%   $273.4052   $273.41   $273.40   $273.40  
  Purchase #6 $242.63   8.170%   $262.4529   $262.45   $262.45   $262.50  
  Purchase #7 $222.87   4.827%   $233.6279   $233.63   $233.65   $233.60  
  7 purchase totals = $1,142.20       $1,232.8916   $1,232.89   $1,232.95   $1,232.90