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 $85.48   12.656%   $96.2983   $96.30   $96.30   $96.30  
  Purchase #2 $66.95   10.553%   $74.0152   $74.02   $74.00   $74.00  
  Purchase #3 $38.55   10.260%   $42.5052   $42.51   $42.50   $42.50  
  Purchase #4 $236.86   13.689%   $269.2838   $269.28   $269.30   $269.30  
  Purchase #5 $227.66   12.736%   $256.6548   $256.65   $256.65   $256.70  
  Purchase #6 $25.42   8.333%   $27.5382   $27.54   $27.55   $27.50  
  Purchase #7 $156.37   12.306%   $175.6129   $175.61   $175.60   $175.60  
  7 purchase totals = $837.29       $941.9084   $941.91   $941.90   $941.90