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 $204.55   10.604%   $226.2405   $226.24   $226.25   $226.20  
  Purchase #2 $164.58   12.838%   $185.7088   $185.71   $185.70   $185.70  
  Purchase #3 $42.27   13.843%   $48.1214   $48.12   $48.10   $48.10  
  Purchase #4 $114.45   11.609%   $127.7365   $127.74   $127.75   $127.70  
  Purchase #5 $244.29   9.219%   $266.8111   $266.81   $266.80   $266.80  
  Purchase #6 $160.89   12.857%   $181.5756   $181.58   $181.60   $181.60  
  Purchase #7 $111.62   9.432%   $122.148   $122.15   $122.15   $122.10  
  7 purchase totals = $1,042.65       $1,158.3419   $1,158.35   $1,158.35   $1,158.20