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 $59.76   12.128%   $67.0077   $67.01   $67.00   $67.00  
  Purchase #2 $102.76   7.686%   $110.6581   $110.66   $110.65   $110.70  
  Purchase #3 $226.83   5.455%   $239.2036   $239.20   $239.20   $239.20  
  Purchase #4 $99.32   12.587%   $111.8214   $111.82   $111.80   $111.80  
  Purchase #5 $237.35   13.187%   $268.6493   $268.65   $268.65   $268.60  
  Purchase #6 $12.27   6.540%   $13.0725   $13.07   $13.05   $13.10  
  Purchase #7 $222.99   3.730%   $231.3075   $231.31   $231.30   $231.30  
  7 purchase totals = $961.28       $1,041.7201   $1,041.72   $1,041.65   $1,041.70