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 $23.83   11.548%   $26.5819   $26.58   $26.60   $26.60  
  Purchase #2 $160.92   6.660%   $171.6373   $171.64   $171.65   $171.60  
  Purchase #3 $107.52   10.782%   $119.1128   $119.11   $119.10   $119.10  
  Purchase #4 $240.35   8.136%   $259.9049   $259.90   $259.90   $259.90  
  Purchase #5 $135.26   11.362%   $150.6282   $150.63   $150.65   $150.60  
  Purchase #6 $45.98   5.264%   $48.4004   $48.40   $48.40   $48.40  
  Purchase #7 $213.44   5.615%   $225.4247   $225.42   $225.40   $225.40  
  7 purchase totals = $927.30       $1,001.6902   $1,001.68   $1,001.70   $1,001.60