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 $237.33   10.757%   $262.8596   $262.86   $262.85   $262.90  
  Purchase #2 $209.95   4.822%   $220.0738   $220.07   $220.05   $220.10  
  Purchase #3 $41.28   7.286%   $44.2877   $44.29   $44.30   $44.30  
  Purchase #4 $174.36   13.455%   $197.8201   $197.82   $197.80   $197.80  
  Purchase #5 $171.68   13.816%   $195.3993   $195.40   $195.40   $195.40  
  Purchase #6 $9.50   11.383%   $10.5814   $10.58   $10.60   $10.60  
  Purchase #7 $150.74   11.190%   $167.6078   $167.61   $167.60   $167.60  
  7 purchase totals = $994.84       $1,098.6297   $1,098.63   $1,098.60   $1,098.70