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 $160.82   13.758%   $182.9456   $182.95   $182.95   $182.90  
  Purchase #2 $11.69   12.515%   $13.153   $13.15   $13.15   $13.20  
  Purchase #3 $224.92   11.483%   $250.7476   $250.75   $250.75   $250.70  
  Purchase #4 $247.64   10.661%   $274.0409   $274.04   $274.05   $274.00  
  Purchase #5 $205.33   11.346%   $228.6267   $228.63   $228.65   $228.60  
  Purchase #6 $76.54   4.659%   $80.106   $80.11   $80.10   $80.10  
  Purchase #7 $92.72   10.322%   $102.2906   $102.29   $102.30   $102.30  
  7 purchase totals = $1,019.66       $1,131.9104   $1,131.92   $1,131.95   $1,131.80