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 $49.57   5.317%   $52.2056   $52.21   $52.20   $52.20  
  Purchase #2 $213.99   10.158%   $235.7271   $235.73   $235.75   $235.70  
  Purchase #3 $113.92   11.473%   $126.99   $126.99   $127.00   $127.00  
  Purchase #4 $201.65   10.617%   $223.0592   $223.06   $223.05   $223.10  
  Purchase #5 $47.56   8.565%   $51.6335   $51.63   $51.65   $51.60  
  Purchase #6 $243.57   9.588%   $266.9235   $266.92   $266.90   $266.90  
  Purchase #7 $87.39   13.364%   $99.0688   $99.07   $99.05   $99.10  
  7 purchase totals = $957.65       $1,055.6077   $1,055.61   $1,055.60   $1,055.60