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 $89.27   12.241%   $100.1975   $100.20   $100.20   $100.20  
  Purchase #2 $216.57   3.293%   $223.7017   $223.70   $223.70   $223.70  
  Purchase #3 $204.42   4.436%   $213.4881   $213.49   $213.50   $213.50  
  Purchase #4 $112.89   11.660%   $126.053   $126.05   $126.05   $126.10  
  Purchase #5 $123.59   3.231%   $127.5832   $127.58   $127.60   $127.60  
  Purchase #6 $207.31   13.460%   $235.2139   $235.21   $235.20   $235.20  
  Purchase #7 $249.75   7.674%   $268.9158   $268.92   $268.90   $268.90  
  7 purchase totals = $1,203.80       $1,295.1532   $1,295.15   $1,295.15   $1,295.20