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 $54.80   12.602%   $61.7059   $61.71   $61.70   $61.70  
  Purchase #2 $205.60   6.866%   $219.7165   $219.72   $219.70   $219.70  
  Purchase #3 $100.66   12.577%   $113.32   $113.32   $113.30   $113.30  
  Purchase #4 $194.70   8.802%   $211.8375   $211.84   $211.85   $211.80  
  Purchase #5 $21.75   10.487%   $24.0309   $24.03   $24.05   $24.00  
  Purchase #6 $162.69   6.728%   $173.6358   $173.64   $173.65   $173.60  
  Purchase #7 $211.76   8.834%   $230.4669   $230.47   $230.45   $230.50  
  7 purchase totals = $951.96       $1,034.7135   $1,034.73   $1,034.70   $1,034.60