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 $217.47   11.782%   $243.0923   $243.09   $243.10   $243.10  
  Purchase #2 $84.31   13.775%   $95.9237   $95.92   $95.90   $95.90  
  Purchase #3 $101.35   10.433%   $111.9238   $111.92   $111.90   $111.90  
  Purchase #4 $145.74   6.189%   $154.7598   $154.76   $154.75   $154.80  
  Purchase #5 $105.80   6.333%   $112.5003   $112.50   $112.50   $112.50  
  Purchase #6 $192.48   4.524%   $201.1878   $201.19   $201.20   $201.20  
  Purchase #7 $226.32   3.589%   $234.4426   $234.44   $234.45   $234.40  
  7 purchase totals = $1,073.47       $1,153.8303   $1,153.82   $1,153.80   $1,153.80