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 $225.37   11.461%   $251.1997   $251.20   $251.20   $251.20  
  Purchase #2 $165.68   10.267%   $182.6904   $182.69   $182.70   $182.70  
  Purchase #3 $194.90   10.803%   $215.955   $215.96   $215.95   $216.00  
  Purchase #4 $72.70   4.854%   $76.2289   $76.23   $76.25   $76.20  
  Purchase #5 $206.25   3.119%   $212.6829   $212.68   $212.70   $212.70  
  Purchase #6 $174.70   5.629%   $184.5339   $184.53   $184.55   $184.50  
  Purchase #7 $189.70   6.218%   $201.4955   $201.50   $201.50   $201.50  
  7 purchase totals = $1,229.30       $1,324.7863   $1,324.79   $1,324.85   $1,324.80