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 $41.96   8.714%   $45.6164   $45.62   $45.60   $45.60  
  Purchase #2 $234.77   4.646%   $245.6774   $245.68   $245.70   $245.70  
  Purchase #3 $237.99   6.827%   $254.2376   $254.24   $254.25   $254.20  
  Purchase #4 $177.48   3.564%   $183.8054   $183.81   $183.80   $183.80  
  Purchase #5 $113.37   4.866%   $118.8866   $118.89   $118.90   $118.90  
  Purchase #6 $16.32   8.203%   $17.6587   $17.66   $17.65   $17.70  
  Purchase #7 $155.45   10.843%   $172.3054   $172.31   $172.30   $172.30  
  7 purchase totals = $977.34       $1,038.1875   $1,038.21   $1,038.20   $1,038.20