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 $143.47   7.812%   $154.6779   $154.68   $154.70   $154.70  
  Purchase #2 $151.86   11.187%   $168.8486   $168.85   $168.85   $168.80  
  Purchase #3 $111.67   12.555%   $125.6902   $125.69   $125.70   $125.70  
  Purchase #4 $202.77   13.756%   $230.663   $230.66   $230.65   $230.70  
  Purchase #5 $59.97   4.732%   $62.8078   $62.81   $62.80   $62.80  
  Purchase #6 $180.96   13.297%   $205.0223   $205.02   $205.00   $205.00  
  Purchase #7 $59.99   11.778%   $67.0556   $67.06   $67.05   $67.10  
  7 purchase totals = $910.69       $1,014.7654   $1,014.77   $1,014.75   $1,014.80