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 $24.81   5.698%   $26.2237   $26.22   $26.20   $26.20  
  Purchase #2 $208.92   9.509%   $228.7862   $228.79   $228.80   $228.80  
  Purchase #3 $160.96   3.489%   $166.5759   $166.58   $166.60   $166.60  
  Purchase #4 $224.82   8.820%   $244.6491   $244.65   $244.65   $244.60  
  Purchase #5 $8.44   9.225%   $9.2186   $9.22   $9.20   $9.20  
  Purchase #6 $32.86   12.757%   $37.052   $37.05   $37.05   $37.10  
  Purchase #7 $233.50   3.314%   $241.2382   $241.24   $241.25   $241.20  
  7 purchase totals = $894.31       $953.7437   $953.75   $953.75   $953.70