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 $31.84   4.410%   $33.2441   $33.24   $33.25   $33.20  
  Purchase #2 $233.68   13.679%   $265.6451   $265.65   $265.65   $265.60  
  Purchase #3 $193.51   5.522%   $204.1956   $204.20   $204.20   $204.20  
  Purchase #4 $99.67   10.166%   $109.8025   $109.80   $109.80   $109.80  
  Purchase #5 $244.87   3.213%   $252.7377   $252.74   $252.75   $252.70  
  Purchase #6 $248.66   8.849%   $270.6639   $270.66   $270.65   $270.70  
  Purchase #7 $65.73   3.182%   $67.8215   $67.82   $67.80   $67.80  
  7 purchase totals = $1,117.96       $1,204.1104   $1,204.11   $1,204.10   $1,204.00