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 $245.99   8.668%   $267.3124   $267.31   $267.30   $267.30  
  Purchase #2 $238.27   6.579%   $253.9458   $253.95   $253.95   $253.90  
  Purchase #3 $196.36   8.195%   $212.4517   $212.45   $212.45   $212.50  
  Purchase #4 $234.65   3.145%   $242.0297   $242.03   $242.05   $242.00  
  Purchase #5 $65.67   6.471%   $69.9195   $69.92   $69.90   $69.90  
  Purchase #6 $53.77   5.693%   $56.8311   $56.83   $56.85   $56.80  
  Purchase #7 $14.50   7.519%   $15.5903   $15.59   $15.60   $15.60  
  7 purchase totals = $1,049.21       $1,118.0805   $1,118.08   $1,118.10   $1,118.00