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 $249.35   12.674%   $280.9526   $280.95   $280.95   $281.00  
  Purchase #2 $90.58   7.438%   $97.3173   $97.32   $97.30   $97.30  
  Purchase #3 $177.34   12.705%   $199.871   $199.87   $199.85   $199.90  
  Purchase #4 $57.35   9.438%   $62.7627   $62.76   $62.75   $62.80  
  Purchase #5 $135.52   5.728%   $143.2826   $143.28   $143.30   $143.30  
  Purchase #6 $212.39   7.225%   $227.7352   $227.74   $227.75   $227.70  
  Purchase #7 $193.55   4.498%   $202.2559   $202.26   $202.25   $202.30  
  7 purchase totals = $1,116.08       $1,214.1773   $1,214.18   $1,214.15   $1,214.30