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 $167.40   11.707%   $186.9975   $187.00   $187.00   $187.00  
  Purchase #2 $105.86   12.329%   $118.9115   $118.91   $118.90   $118.90  
  Purchase #3 $100.51   5.380%   $105.9174   $105.92   $105.90   $105.90  
  Purchase #4 $24.39   10.208%   $26.8797   $26.88   $26.90   $26.90  
  Purchase #5 $98.40   3.865%   $102.2032   $102.20   $102.20   $102.20  
  Purchase #6 $21.30   10.822%   $23.6051   $23.61   $23.60   $23.60  
  Purchase #7 $212.32   11.474%   $236.6816   $236.68   $236.70   $236.70  
  7 purchase totals = $730.18       $801.1960   $801.20   $801.20   $801.20