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 $68.51   7.429%   $73.5996   $73.60   $73.60   $73.60  
  Purchase #2 $81.80   13.723%   $93.0254   $93.03   $93.05   $93.00  
  Purchase #3 $235.29   8.812%   $256.0238   $256.02   $256.00   $256.00  
  Purchase #4 $224.57   12.514%   $252.6727   $252.67   $252.65   $252.70  
  Purchase #5 $247.56   10.224%   $272.8705   $272.87   $272.85   $272.90  
  Purchase #6 $105.67   6.121%   $112.1381   $112.14   $112.15   $112.10  
  Purchase #7 $60.34   13.872%   $68.7104   $68.71   $68.70   $68.70  
  7 purchase totals = $1,023.74       $1,129.0405   $1,129.04   $1,129.00   $1,129.00