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 $55.26   8.575%   $59.9985   $60.00   $60.00   $60.00  
  Purchase #2 $152.67   6.623%   $162.7813   $162.78   $162.80   $162.80  
  Purchase #3 $81.85   12.343%   $91.9527   $91.95   $91.95   $92.00  
  Purchase #4 $225.26   5.544%   $237.7484   $237.75   $237.75   $237.70  
  Purchase #5 $149.25   12.199%   $167.457   $167.46   $167.45   $167.50  
  Purchase #6 $156.29   5.515%   $164.9094   $164.91   $164.90   $164.90  
  Purchase #7 $194.69   11.152%   $216.4018   $216.40   $216.40   $216.40  
  7 purchase totals = $1,015.27       $1,101.2491   $1,101.25   $1,101.25   $1,101.30