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 $152.95   6.356%   $162.6715   $162.67   $162.65   $162.70  
  Purchase #2 $32.69   4.384%   $34.1231   $34.12   $34.10   $34.10  
  Purchase #3 $129.77   4.618%   $135.7628   $135.76   $135.75   $135.80  
  Purchase #4 $104.60   11.694%   $116.8319   $116.83   $116.85   $116.80  
  Purchase #5 $247.68   8.520%   $268.7823   $268.78   $268.80   $268.80  
  Purchase #6 $32.40   3.280%   $33.4627   $33.46   $33.45   $33.50  
  Purchase #7 $200.36   5.501%   $211.3818   $211.38   $211.40   $211.40  
  7 purchase totals = $900.45       $963.0161   $963.00   $963.00   $963.10