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 $84.50   12.222%   $94.8276   $94.83   $94.85   $94.80  
  Purchase #2 $233.97   9.803%   $256.9061   $256.91   $256.90   $256.90  
  Purchase #3 $196.57   7.310%   $210.9393   $210.94   $210.95   $210.90  
  Purchase #4 $192.61   4.612%   $201.4932   $201.49   $201.50   $201.50  
  Purchase #5 $114.60   10.230%   $126.3236   $126.32   $126.30   $126.30  
  Purchase #6 $101.73   11.214%   $113.138   $113.14   $113.15   $113.10  
  Purchase #7 $7.65   4.827%   $8.0193   $8.02   $8.00   $8.00  
  7 purchase totals = $931.63       $1,011.6471   $1,011.65   $1,011.65   $1,011.50