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 $162.62   9.513%   $178.09   $178.09   $178.10   $178.10  
  Purchase #2 $228.47   13.367%   $259.0096   $259.01   $259.00   $259.00  
  Purchase #3 $64.85   4.431%   $67.7235   $67.72   $67.70   $67.70  
  Purchase #4 $5.73   12.260%   $6.4325   $6.43   $6.45   $6.40  
  Purchase #5 $235.83   12.651%   $265.6649   $265.66   $265.65   $265.70  
  Purchase #6 $19.39   11.607%   $21.6406   $21.64   $21.65   $21.60  
  Purchase #7 $148.54   8.842%   $161.6739   $161.67   $161.65   $161.70  
  7 purchase totals = $865.43       $960.2350   $960.22   $960.20   $960.20