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 $51.44   7.273%   $55.1812   $55.18   $55.20   $55.20  
  Purchase #2 $104.89   5.242%   $110.3883   $110.39   $110.40   $110.40  
  Purchase #3 $113.73   9.461%   $124.49   $124.49   $124.50   $124.50  
  Purchase #4 $166.45   6.192%   $176.7566   $176.76   $176.75   $176.80  
  Purchase #5 $244.45   3.524%   $253.0644   $253.06   $253.05   $253.10  
  Purchase #6 $77.66   7.200%   $83.2515   $83.25   $83.25   $83.30  
  Purchase #7 $221.27   9.458%   $242.1977   $242.20   $242.20   $242.20  
  7 purchase totals = $979.89       $1,045.3297   $1,045.33   $1,045.35   $1,045.50