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 $130.27   5.366%   $137.2603   $137.26   $137.25   $137.30  
  Purchase #2 $211.31   7.380%   $226.9047   $226.90   $226.90   $226.90  
  Purchase #3 $235.33   3.740%   $244.1313   $244.13   $244.15   $244.10  
  Purchase #4 $64.30   9.396%   $70.3416   $70.34   $70.35   $70.30  
  Purchase #5 $137.88   13.335%   $156.2663   $156.27   $156.25   $156.30  
  Purchase #6 $178.79   9.359%   $195.523   $195.52   $195.50   $195.50  
  Purchase #7 $228.32   3.617%   $236.5783   $236.58   $236.60   $236.60  
  7 purchase totals = $1,186.20       $1,267.0055   $1,267.00   $1,267.00   $1,267.00