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 $246.79   3.716%   $255.9607   $255.96   $255.95   $256.00  
  Purchase #2 $84.46   12.422%   $94.9516   $94.95   $94.95   $95.00  
  Purchase #3 $148.35   11.592%   $165.5467   $165.55   $165.55   $165.50  
  Purchase #4 $67.49   3.128%   $69.6011   $69.60   $69.60   $69.60  
  Purchase #5 $147.49   6.338%   $156.8379   $156.84   $156.85   $156.80  
  Purchase #6 $108.67   10.727%   $120.327   $120.33   $120.35   $120.30  
  Purchase #7 $38.94   3.383%   $40.2573   $40.26   $40.25   $40.30  
  7 purchase totals = $842.19       $903.4823   $903.49   $903.50   $903.50