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 $242.97   4.862%   $254.7832   $254.78   $254.80   $254.80  
  Purchase #2 $70.58   3.408%   $72.9854   $72.99   $73.00   $73.00  
  Purchase #3 $155.66   6.108%   $165.1677   $165.17   $165.15   $165.20  
  Purchase #4 $39.67   7.106%   $42.489   $42.49   $42.50   $42.50  
  Purchase #5 $245.80   7.425%   $264.0507   $264.05   $264.05   $264.10  
  Purchase #6 $151.94   10.662%   $168.1398   $168.14   $168.15   $168.10  
  Purchase #7 $222.74   6.221%   $236.5967   $236.60   $236.60   $236.60  
  7 purchase totals = $1,129.36       $1,204.2125   $1,204.22   $1,204.25   $1,204.30