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 $218.87   4.376%   $228.4478   $228.45   $228.45   $228.40  
  Purchase #2 $104.70   12.499%   $117.7865   $117.79   $117.80   $117.80  
  Purchase #3 $51.83   8.180%   $56.0697   $56.07   $56.05   $56.10  
  Purchase #4 $161.39   7.350%   $173.2522   $173.25   $173.25   $173.30  
  Purchase #5 $141.51   13.352%   $160.4044   $160.40   $160.40   $160.40  
  Purchase #6 $49.86   11.152%   $55.4204   $55.42   $55.40   $55.40  
  Purchase #7 $73.99   12.859%   $83.5044   $83.50   $83.50   $83.50  
  7 purchase totals = $802.15       $874.8854   $874.88   $874.85   $874.90