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 $146.94   8.528%   $159.471   $159.47   $159.45   $159.50  
  Purchase #2 $198.38   3.342%   $205.0099   $205.01   $205.00   $205.00  
  Purchase #3 $87.94   6.839%   $93.9542   $93.95   $93.95   $94.00  
  Purchase #4 $81.56   6.554%   $86.9054   $86.91   $86.90   $86.90  
  Purchase #5 $174.44   10.444%   $192.6585   $192.66   $192.65   $192.70  
  Purchase #6 $155.48   7.732%   $167.5017   $167.50   $167.50   $167.50  
  Purchase #7 $128.57   5.522%   $135.6696   $135.67   $135.65   $135.70  
  7 purchase totals = $973.31       $1,041.1703   $1,041.17   $1,041.10   $1,041.30