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 $204.93   13.857%   $233.3272   $233.33   $233.35   $233.30  
  Purchase #2 $32.29   3.338%   $33.3678   $33.37   $33.35   $33.40  
  Purchase #3 $201.37   8.667%   $218.8227   $218.82   $218.80   $218.80  
  Purchase #4 $228.40   7.707%   $246.0028   $246.00   $246.00   $246.00  
  Purchase #5 $183.95   7.591%   $197.9136   $197.91   $197.90   $197.90  
  Purchase #6 $98.65   6.823%   $105.3809   $105.38   $105.40   $105.40  
  Purchase #7 $20.91   10.226%   $23.0483   $23.05   $23.05   $23.00  
  7 purchase totals = $970.50       $1,057.8633   $1,057.86   $1,057.85   $1,057.80