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 $182.63   11.127%   $202.9512   $202.95   $202.95   $203.00  
  Purchase #2 $156.44   5.346%   $164.8033   $164.80   $164.80   $164.80  
  Purchase #3 $10.59   11.842%   $11.8441   $11.84   $11.85   $11.80  
  Purchase #4 $133.59   6.128%   $141.7764   $141.78   $141.80   $141.80  
  Purchase #5 $156.93   11.512%   $174.9958   $175.00   $175.00   $175.00  
  Purchase #6 $246.67   7.673%   $265.597   $265.60   $265.60   $265.60  
  Purchase #7 $199.37   8.518%   $216.3523   $216.35   $216.35   $216.40  
  7 purchase totals = $1,086.22       $1,178.3201   $1,178.32   $1,178.35   $1,178.40