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 $61.79   8.530%   $67.0607   $67.06   $67.05   $67.10  
  Purchase #2 $157.39   11.803%   $175.9667   $175.97   $175.95   $176.00  
  Purchase #3 $180.30   9.363%   $197.1815   $197.18   $197.20   $197.20  
  Purchase #4 $226.68   8.827%   $246.689   $246.69   $246.70   $246.70  
  Purchase #5 $131.25   4.103%   $136.6352   $136.64   $136.65   $136.60  
  Purchase #6 $32.62   3.214%   $33.6684   $33.67   $33.65   $33.70  
  Purchase #7 $69.41   11.383%   $77.3109   $77.31   $77.30   $77.30  
  7 purchase totals = $859.44       $934.5124   $934.52   $934.50   $934.60