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 $42.44   8.776%   $46.1645   $46.16   $46.15   $46.20  
  Purchase #2 $41.73   9.766%   $45.8054   $45.81   $45.80   $45.80  
  Purchase #3 $241.88   8.323%   $262.0117   $262.01   $262.00   $262.00  
  Purchase #4 $32.25   6.766%   $34.432   $34.43   $34.45   $34.40  
  Purchase #5 $98.48   9.823%   $108.1537   $108.15   $108.15   $108.20  
  Purchase #6 $150.40   7.686%   $161.9597   $161.96   $161.95   $162.00  
  Purchase #7 $92.58   6.333%   $98.4431   $98.44   $98.45   $98.40  
  7 purchase totals = $699.76       $756.9701   $756.96   $756.95   $757.00