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 $57.92   6.737%   $61.8221   $61.82   $61.80   $61.80  
  Purchase #2 $131.85   4.308%   $137.5301   $137.53   $137.55   $137.50  
  Purchase #3 $219.79   11.297%   $244.6197   $244.62   $244.60   $244.60  
  Purchase #4 $243.74   7.286%   $261.4989   $261.50   $261.50   $261.50  
  Purchase #5 $27.56   12.408%   $30.9796   $30.98   $31.00   $31.00  
  Purchase #6 $22.65   7.526%   $24.3546   $24.35   $24.35   $24.40  
  Purchase #7 $185.99   10.260%   $205.0726   $205.07   $205.05   $205.10  
  7 purchase totals = $889.50       $965.8776   $965.87   $965.85   $965.90