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 $191.79   5.239%   $201.8379   $201.84   $201.85   $201.80  
  Purchase #2 $85.87   6.789%   $91.6997   $91.70   $91.70   $91.70  
  Purchase #3 $165.63   7.298%   $177.7177   $177.72   $177.70   $177.70  
  Purchase #4 $156.36   3.848%   $162.3767   $162.38   $162.40   $162.40  
  Purchase #5 $79.64   6.123%   $84.5164   $84.52   $84.50   $84.50  
  Purchase #6 $117.42   6.747%   $125.3423   $125.34   $125.35   $125.30  
  Purchase #7 $147.69   7.824%   $159.2453   $159.25   $159.25   $159.20  
  7 purchase totals = $944.40       $1,002.7360   $1,002.75   $1,002.75   $1,002.60