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 $216.48   11.733%   $241.8796   $241.88   $241.90   $241.90  
  Purchase #2 $16.58   3.385%   $17.1412   $17.14   $17.15   $17.10  
  Purchase #3 $11.35   7.627%   $12.2157   $12.22   $12.20   $12.20  
  Purchase #4 $59.56   4.564%   $62.2783   $62.28   $62.30   $62.30  
  Purchase #5 $15.41   5.865%   $16.3138   $16.31   $16.30   $16.30  
  Purchase #6 $151.97   5.285%   $160.0016   $160.00   $160.00   $160.00  
  Purchase #7 $235.81   4.843%   $247.2303   $247.23   $247.25   $247.20  
  7 purchase totals = $707.16       $757.0605   $757.06   $757.10   $757.00