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 $213.89   6.630%   $228.0709   $228.07   $228.05   $228.10  
  Purchase #2 $131.93   12.456%   $148.3632   $148.36   $148.35   $148.40  
  Purchase #3 $81.51   11.807%   $91.1339   $91.13   $91.15   $91.10  
  Purchase #4 $81.74   5.599%   $86.3166   $86.32   $86.30   $86.30  
  Purchase #5 $226.58   11.426%   $252.469   $252.47   $252.45   $252.50  
  Purchase #6 $213.52   10.527%   $235.9973   $236.00   $236.00   $236.00  
  Purchase #7 $170.55   7.733%   $183.7386   $183.74   $183.75   $183.70  
  7 purchase totals = $1,119.72       $1,226.0895   $1,226.09   $1,226.05   $1,226.10