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 $235.66   13.432%   $267.3139   $267.31   $267.30   $267.30  
  Purchase #2 $72.63   5.400%   $76.552   $76.55   $76.55   $76.60  
  Purchase #3 $207.34   5.389%   $218.5136   $218.51   $218.50   $218.50  
  Purchase #4 $31.74   13.280%   $35.9551   $35.96   $35.95   $36.00  
  Purchase #5 $240.53   9.355%   $263.0316   $263.03   $263.05   $263.00  
  Purchase #6 $155.50   11.424%   $173.2643   $173.26   $173.25   $173.30  
  Purchase #7 $250.26   7.498%   $269.0245   $269.02   $269.00   $269.00  
  7 purchase totals = $1,193.66       $1,303.6550   $1,303.64   $1,303.60   $1,303.70