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 $14.87   8.482%   $16.1313   $16.13   $16.15   $16.10  
  Purchase #2 $192.98   11.841%   $215.8308   $215.83   $215.85   $215.80  
  Purchase #3 $201.47   8.359%   $218.3109   $218.31   $218.30   $218.30  
  Purchase #4 $220.32   9.386%   $240.9992   $241.00   $241.00   $241.00  
  Purchase #5 $230.77   6.448%   $245.65   $245.65   $245.65   $245.70  
  Purchase #6 $230.32   10.771%   $255.1278   $255.13   $255.15   $255.10  
  Purchase #7 $9.96   12.677%   $11.2226   $11.22   $11.20   $11.20  
  7 purchase totals = $1,100.69       $1,203.2726   $1,203.27   $1,203.30   $1,203.20