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 $69.88   9.620%   $76.6025   $76.60   $76.60   $76.60  
  Purchase #2 $132.41   11.401%   $147.5061   $147.51   $147.50   $147.50  
  Purchase #3 $239.89   10.518%   $265.1216   $265.12   $265.10   $265.10  
  Purchase #4 $36.78   10.583%   $40.6724   $40.67   $40.65   $40.70  
  Purchase #5 $12.61   10.869%   $13.9806   $13.98   $14.00   $14.00  
  Purchase #6 $51.62   3.165%   $53.2538   $53.25   $53.25   $53.30  
  Purchase #7 $206.46   11.779%   $230.7789   $230.78   $230.80   $230.80  
  7 purchase totals = $749.65       $827.9159   $827.91   $827.90   $828.00