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 $118.53   12.743%   $133.6343   $133.63   $133.65   $133.60  
  Purchase #2 $54.60   11.776%   $61.0297   $61.03   $61.05   $61.00  
  Purchase #3 $237.90   8.874%   $259.0112   $259.01   $259.00   $259.00  
  Purchase #4 $13.41   4.712%   $14.0419   $14.04   $14.05   $14.00  
  Purchase #5 $120.85   13.406%   $137.0512   $137.05   $137.05   $137.10  
  Purchase #6 $249.75   13.697%   $283.9583   $283.96   $283.95   $284.00  
  Purchase #7 $200.63   8.733%   $218.151   $218.15   $218.15   $218.20  
  7 purchase totals = $995.67       $1,106.8776   $1,106.87   $1,106.90   $1,106.90