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 $211.34   8.200%   $228.6699   $228.67   $228.65   $228.70  
  Purchase #2 $167.75   6.131%   $178.0348   $178.03   $178.05   $178.00  
  Purchase #3 $119.68   4.551%   $125.1266   $125.13   $125.15   $125.10  
  Purchase #4 $134.98   5.832%   $142.852   $142.85   $142.85   $142.90  
  Purchase #5 $167.41   6.635%   $178.5177   $178.52   $178.50   $178.50  
  Purchase #6 $33.27   6.286%   $35.3614   $35.36   $35.35   $35.40  
  Purchase #7 $105.77   6.667%   $112.8217   $112.82   $112.80   $112.80  
  7 purchase totals = $940.20       $1,001.3841   $1,001.38   $1,001.35   $1,001.40