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 $114.99   8.327%   $124.5652   $124.57   $124.55   $124.60  
  Purchase #2 $164.77   12.276%   $184.9972   $185.00   $185.00   $185.00  
  Purchase #3 $70.28   4.573%   $73.4939   $73.49   $73.50   $73.50  
  Purchase #4 $212.79   13.661%   $241.8592   $241.86   $241.85   $241.90  
  Purchase #5 $170.84   13.198%   $193.3875   $193.39   $193.40   $193.40  
  Purchase #6 $101.58   4.387%   $106.0363   $106.04   $106.05   $106.00  
  Purchase #7 $58.46   9.218%   $63.8488   $63.85   $63.85   $63.80  
  7 purchase totals = $893.71       $988.1881   $988.20   $988.20   $988.20