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 $206.93   12.670%   $233.148   $233.15   $233.15   $233.10  
  Purchase #2 $92.86   4.293%   $96.8465   $96.85   $96.85   $96.80  
  Purchase #3 $216.68   5.487%   $228.5692   $228.57   $228.55   $228.60  
  Purchase #4 $24.26   10.616%   $26.8354   $26.84   $26.85   $26.80  
  Purchase #5 $94.41   5.770%   $99.8575   $99.86   $99.85   $99.90  
  Purchase #6 $58.26   5.422%   $61.4189   $61.42   $61.40   $61.40  
  Purchase #7 $92.61   9.284%   $101.2079   $101.21   $101.20   $101.20  
  7 purchase totals = $786.01       $847.8834   $847.90   $847.85   $847.80