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 $143.87   10.549%   $159.0468   $159.05   $159.05   $159.00  
  Purchase #2 $149.68   3.109%   $154.3336   $154.33   $154.35   $154.30  
  Purchase #3 $48.65   12.477%   $54.7201   $54.72   $54.70   $54.70  
  Purchase #4 $201.94   5.543%   $213.1335   $213.13   $213.15   $213.10  
  Purchase #5 $168.63   13.435%   $191.2854   $191.29   $191.30   $191.30  
  Purchase #6 $30.67   3.721%   $31.8112   $31.81   $31.80   $31.80  
  Purchase #7 $203.58   5.466%   $214.7077   $214.71   $214.70   $214.70  
  7 purchase totals = $947.02       $1,019.0383   $1,019.04   $1,019.05   $1,018.90