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 $167.27   9.192%   $182.6455   $182.65   $182.65   $182.60  
  Purchase #2 $168.33   3.281%   $173.8529   $173.85   $173.85   $173.90  
  Purchase #3 $16.71   6.128%   $17.734   $17.73   $17.75   $17.70  
  Purchase #4 $206.84   11.144%   $229.8902   $229.89   $229.90   $229.90  
  Purchase #5 $237.33   4.195%   $247.286   $247.29   $247.30   $247.30  
  Purchase #6 $67.27   13.195%   $76.1463   $76.15   $76.15   $76.10  
  Purchase #7 $83.49   12.203%   $93.6783   $93.68   $93.70   $93.70  
  7 purchase totals = $947.24       $1,021.2332   $1,021.24   $1,021.30   $1,021.20