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 $212.68   13.811%   $242.0532   $242.05   $242.05   $242.10  
  Purchase #2 $200.66   9.463%   $219.6485   $219.65   $219.65   $219.60  
  Purchase #3 $69.36   11.272%   $77.1783   $77.18   $77.20   $77.20  
  Purchase #4 $98.83   5.726%   $104.489   $104.49   $104.50   $104.50  
  Purchase #5 $40.33   11.524%   $44.9776   $44.98   $45.00   $45.00  
  Purchase #6 $52.31   8.502%   $56.7574   $56.76   $56.75   $56.80  
  Purchase #7 $133.31   7.292%   $143.031   $143.03   $143.05   $143.00  
  7 purchase totals = $807.48       $888.1350   $888.14   $888.20   $888.20