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 $61.75   8.694%   $67.1185   $67.12   $67.10   $67.10  
  Purchase #2 $14.72   10.771%   $16.3055   $16.31   $16.30   $16.30  
  Purchase #3 $62.66   13.289%   $70.9869   $70.99   $71.00   $71.00  
  Purchase #4 $15.39   13.805%   $17.5146   $17.51   $17.50   $17.50  
  Purchase #5 $25.71   3.802%   $26.6875   $26.69   $26.70   $26.70  
  Purchase #6 $122.93   8.406%   $133.2635   $133.26   $133.25   $133.30  
  Purchase #7 $74.33   11.670%   $83.0043   $83.00   $83.00   $83.00  
  7 purchase totals = $377.49       $414.8808   $414.88   $414.85   $414.90