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 $212.39   12.743%   $239.4549   $239.45   $239.45   $239.50  
  Purchase #2 $144.68   4.354%   $150.9794   $150.98   $151.00   $151.00  
  Purchase #3 $82.36   12.548%   $92.6945   $92.69   $92.70   $92.70  
  Purchase #4 $248.98   12.396%   $279.8436   $279.84   $279.85   $279.80  
  Purchase #5 $20.65   6.274%   $21.9456   $21.95   $21.95   $21.90  
  Purchase #6 $143.68   3.718%   $149.022   $149.02   $149.00   $149.00  
  Purchase #7 $75.50   6.680%   $80.5434   $80.54   $80.55   $80.50  
  7 purchase totals = $928.24       $1,014.4834   $1,014.47   $1,014.50   $1,014.40