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 $243.80   10.457%   $269.2942   $269.29   $269.30   $269.30  
  Purchase #2 $15.87   3.111%   $16.3637   $16.36   $16.35   $16.40  
  Purchase #3 $194.65   4.112%   $202.654   $202.65   $202.65   $202.70  
  Purchase #4 $165.61   12.767%   $186.7534   $186.75   $186.75   $186.80  
  Purchase #5 $34.32   5.222%   $36.1122   $36.11   $36.10   $36.10  
  Purchase #6 $205.30   9.191%   $224.1691   $224.17   $224.15   $224.20  
  Purchase #7 $95.29   12.526%   $107.226   $107.23   $107.25   $107.20  
  7 purchase totals = $954.84       $1,042.5726   $1,042.56   $1,042.55   $1,042.70