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 $206.74   9.206%   $225.7725   $225.77   $225.75   $225.80  
  Purchase #2 $187.53   8.731%   $203.9032   $203.90   $203.90   $203.90  
  Purchase #3 $144.26   13.276%   $163.412   $163.41   $163.40   $163.40  
  Purchase #4 $213.90   4.258%   $223.0079   $223.01   $223.00   $223.00  
  Purchase #5 $164.67   12.397%   $185.0841   $185.08   $185.10   $185.10  
  Purchase #6 $54.44   11.380%   $60.6353   $60.64   $60.65   $60.60  
  Purchase #7 $152.67   3.407%   $157.8715   $157.87   $157.85   $157.90  
  7 purchase totals = $1,124.21       $1,219.6865   $1,219.68   $1,219.65   $1,219.70