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 $41.81   13.236%   $47.344   $47.34   $47.35   $47.30  
  Purchase #2 $56.99   3.511%   $58.9909   $58.99   $59.00   $59.00  
  Purchase #3 $194.68   4.110%   $202.6813   $202.68   $202.70   $202.70  
  Purchase #4 $26.78   13.199%   $30.3147   $30.31   $30.30   $30.30  
  Purchase #5 $237.72   13.562%   $269.9596   $269.96   $269.95   $270.00  
  Purchase #6 $200.78   9.486%   $219.826   $219.83   $219.85   $219.80  
  Purchase #7 $114.41   11.174%   $127.1942   $127.19   $127.20   $127.20  
  7 purchase totals = $873.17       $956.3107   $956.30   $956.35   $956.30