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 $151.37   8.352%   $164.0124   $164.01   $164.00   $164.00  
  Purchase #2 $244.37   5.316%   $257.3607   $257.36   $257.35   $257.40  
  Purchase #3 $122.55   13.276%   $138.8197   $138.82   $138.80   $138.80  
  Purchase #4 $204.71   12.603%   $230.5096   $230.51   $230.50   $230.50  
  Purchase #5 $7.32   9.271%   $7.9986   $8.00   $8.00   $8.00  
  Purchase #6 $159.94   11.540%   $178.3971   $178.40   $178.40   $178.40  
  Purchase #7 $95.76   3.731%   $99.3328   $99.33   $99.35   $99.30  
  7 purchase totals = $986.02       $1,076.4309   $1,076.43   $1,076.40   $1,076.40