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 $60.36   12.589%   $67.9587   $67.96   $67.95   $68.00  
  Purchase #2 $238.83   8.454%   $259.0207   $259.02   $259.00   $259.00  
  Purchase #3 $31.86   8.669%   $34.6219   $34.62   $34.60   $34.60  
  Purchase #4 $34.72   5.474%   $36.6206   $36.62   $36.60   $36.60  
  Purchase #5 $185.79   11.332%   $206.8437   $206.84   $206.85   $206.80  
  Purchase #6 $221.45   12.244%   $248.5643   $248.56   $248.55   $248.60  
  Purchase #7 $108.36   12.564%   $121.9744   $121.97   $121.95   $122.00  
  7 purchase totals = $881.37       $975.6043   $975.59   $975.50   $975.60