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 $184.87   11.261%   $205.6882   $205.69   $205.70   $205.70  
  Purchase #2 $131.88   12.535%   $148.4112   $148.41   $148.40   $148.40  
  Purchase #3 $126.52   5.715%   $133.7506   $133.75   $133.75   $133.80  
  Purchase #4 $184.76   5.283%   $194.5209   $194.52   $194.50   $194.50  
  Purchase #5 $94.43   13.657%   $107.3263   $107.33   $107.35   $107.30  
  Purchase #6 $229.30   4.230%   $238.9994   $239.00   $239.00   $239.00  
  Purchase #7 $159.46   13.452%   $180.9106   $180.91   $180.90   $180.90  
  7 purchase totals = $1,111.22       $1,209.6072   $1,209.61   $1,209.60   $1,209.60