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 $218.84   11.356%   $243.6915   $243.69   $243.70   $243.70  
  Purchase #2 $202.56   7.559%   $217.8715   $217.87   $217.85   $217.90  
  Purchase #3 $186.26   6.498%   $198.3632   $198.36   $198.35   $198.40  
  Purchase #4 $216.77   5.684%   $229.0912   $229.09   $229.10   $229.10  
  Purchase #5 $98.78   12.727%   $111.3517   $111.35   $111.35   $111.40  
  Purchase #6 $5.48   7.607%   $5.8969   $5.90   $5.90   $5.90  
  Purchase #7 $152.87   9.720%   $167.729   $167.73   $167.75   $167.70  
  7 purchase totals = $1,081.56       $1,173.9950   $1,173.99   $1,174.00   $1,174.10