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 $219.79   12.528%   $247.3253   $247.33   $247.35   $247.30  
  Purchase #2 $131.47   8.855%   $143.1117   $143.11   $143.10   $143.10  
  Purchase #3 $183.73   13.184%   $207.953   $207.95   $207.95   $208.00  
  Purchase #4 $118.91   8.503%   $129.0209   $129.02   $129.00   $129.00  
  Purchase #5 $45.40   8.412%   $49.219   $49.22   $49.20   $49.20  
  Purchase #6 $7.98   13.526%   $9.0594   $9.06   $9.05   $9.10  
  Purchase #7 $244.25   6.353%   $259.7672   $259.77   $259.75   $259.80  
  7 purchase totals = $951.53       $1,045.4565   $1,045.46   $1,045.40   $1,045.50