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 $49.45   11.600%   $55.1862   $55.19   $55.20   $55.20  
  Purchase #2 $94.69   7.389%   $101.6866   $101.69   $101.70   $101.70  
  Purchase #3 $239.76   8.254%   $259.5498   $259.55   $259.55   $259.50  
  Purchase #4 $55.28   8.572%   $60.0186   $60.02   $60.00   $60.00  
  Purchase #5 $52.63   6.619%   $56.1136   $56.11   $56.10   $56.10  
  Purchase #6 $231.96   12.311%   $260.5166   $260.52   $260.50   $260.50  
  Purchase #7 $248.78   8.547%   $270.0432   $270.04   $270.05   $270.00  
  7 purchase totals = $972.55       $1,063.1146   $1,063.12   $1,063.10   $1,063.00