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 $52.80   13.383%   $59.8662   $59.87   $59.85   $59.90  
  Purchase #2 $240.70   4.821%   $252.3041   $252.30   $252.30   $252.30  
  Purchase #3 $194.35   5.842%   $205.7039   $205.70   $205.70   $205.70  
  Purchase #4 $92.52   6.659%   $98.6809   $98.68   $98.70   $98.70  
  Purchase #5 $228.82   7.734%   $246.5169   $246.52   $246.50   $246.50  
  Purchase #6 $126.36   8.767%   $137.438   $137.44   $137.45   $137.40  
  Purchase #7 $183.60   12.545%   $206.6326   $206.63   $206.65   $206.60  
  7 purchase totals = $1,119.15       $1,207.1426   $1,207.14   $1,207.15   $1,207.10