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 $229.33   10.443%   $253.2789   $253.28   $253.30   $253.30  
  Purchase #2 $94.27   3.291%   $97.3724   $97.37   $97.35   $97.40  
  Purchase #3 $167.74   7.277%   $179.9464   $179.95   $179.95   $179.90  
  Purchase #4 $205.47   10.258%   $226.5471   $226.55   $226.55   $226.50  
  Purchase #5 $212.34   6.767%   $226.709   $226.71   $226.70   $226.70  
  Purchase #6 $74.55   4.643%   $78.0114   $78.01   $78.00   $78.00  
  Purchase #7 $216.45   7.597%   $232.8937   $232.89   $232.90   $232.90  
  7 purchase totals = $1,200.15       $1,294.7589   $1,294.76   $1,294.75   $1,294.70