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 $63.88   11.540%   $71.2518   $71.25   $71.25   $71.30  
  Purchase #2 $186.60   6.826%   $199.3373   $199.34   $199.35   $199.30  
  Purchase #3 $223.46   11.417%   $248.9724   $248.97   $248.95   $249.00  
  Purchase #4 $108.40   10.546%   $119.8319   $119.83   $119.85   $119.80  
  Purchase #5 $35.61   5.298%   $37.4966   $37.50   $37.50   $37.50  
  Purchase #6 $234.58   10.615%   $259.4807   $259.48   $259.50   $259.50  
  Purchase #7 $128.59   7.873%   $138.7139   $138.71   $138.70   $138.70  
  7 purchase totals = $981.12       $1,075.0846   $1,075.08   $1,075.10   $1,075.10