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 $82.79   4.127%   $86.2067   $86.21   $86.20   $86.20  
  Purchase #2 $91.73   4.583%   $95.934   $95.93   $95.95   $95.90  
  Purchase #3 $116.94   9.104%   $127.5862   $127.59   $127.60   $127.60  
  Purchase #4 $65.28   3.712%   $67.7032   $67.70   $67.70   $67.70  
  Purchase #5 $203.65   9.573%   $223.1454   $223.15   $223.15   $223.10  
  Purchase #6 $202.48   10.513%   $223.7667   $223.77   $223.75   $223.80  
  Purchase #7 $61.50   12.248%   $69.0325   $69.03   $69.05   $69.00  
  7 purchase totals = $824.37       $893.3747   $893.38   $893.40   $893.30