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 $166.80   11.209%   $185.4966   $185.50   $185.50   $185.50  
  Purchase #2 $129.52   10.274%   $142.8269   $142.83   $142.85   $142.80  
  Purchase #3 $114.93   11.610%   $128.2734   $128.27   $128.25   $128.30  
  Purchase #4 $219.32   8.403%   $237.7495   $237.75   $237.75   $237.70  
  Purchase #5 $30.43   13.281%   $34.4714   $34.47   $34.45   $34.50  
  Purchase #6 $197.86   9.650%   $216.9535   $216.95   $216.95   $217.00  
  Purchase #7 $15.41   6.241%   $16.3717   $16.37   $16.35   $16.40  
  7 purchase totals = $874.27       $962.1430   $962.14   $962.10   $962.20