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 $161.96   9.581%   $177.4774   $177.48   $177.50   $177.50  
  Purchase #2 $124.75   13.300%   $141.3418   $141.34   $141.35   $141.30  
  Purchase #3 $18.36   7.209%   $19.6836   $19.68   $19.70   $19.70  
  Purchase #4 $232.28   7.773%   $250.3351   $250.34   $250.35   $250.30  
  Purchase #5 $237.95   5.636%   $251.3609   $251.36   $251.35   $251.40  
  Purchase #6 $95.46   6.603%   $101.7632   $101.76   $101.75   $101.80  
  Purchase #7 $237.50   12.703%   $267.6696   $267.67   $267.65   $267.70  
  7 purchase totals = $1,108.26       $1,209.6316   $1,209.63   $1,209.65   $1,209.70