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 $58.62   11.732%   $65.4973   $65.50   $65.50   $65.50  
  Purchase #2 $133.52   7.660%   $143.7476   $143.75   $143.75   $143.70  
  Purchase #3 $17.31   12.117%   $19.4075   $19.41   $19.40   $19.40  
  Purchase #4 $54.37   5.328%   $57.2668   $57.27   $57.25   $57.30  
  Purchase #5 $120.74   10.418%   $133.3187   $133.32   $133.30   $133.30  
  Purchase #6 $31.27   4.803%   $32.7719   $32.77   $32.75   $32.80  
  Purchase #7 $244.82   6.523%   $260.7896   $260.79   $260.80   $260.80  
  7 purchase totals = $660.65       $712.7994   $712.81   $712.75   $712.80