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 $60.58   6.378%   $64.4438   $64.44   $64.45   $64.40  
  Purchase #2 $250.52   9.671%   $274.7478   $274.75   $274.75   $274.70  
  Purchase #3 $167.46   4.443%   $174.9002   $174.90   $174.90   $174.90  
  Purchase #4 $203.79   11.141%   $226.4942   $226.49   $226.50   $226.50  
  Purchase #5 $117.84   9.725%   $129.2999   $129.30   $129.30   $129.30  
  Purchase #6 $205.57   9.176%   $224.4331   $224.43   $224.45   $224.40  
  Purchase #7 $170.76   6.222%   $181.3847   $181.38   $181.40   $181.40  
  7 purchase totals = $1,176.52       $1,275.7037   $1,275.69   $1,275.75   $1,275.60