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 $123.87   8.328%   $134.1859   $134.19   $134.20   $134.20  
  Purchase #2 $239.38   10.552%   $264.6394   $264.64   $264.65   $264.60  
  Purchase #3 $139.60   5.285%   $146.9779   $146.98   $147.00   $147.00  
  Purchase #4 $111.91   6.175%   $118.8204   $118.82   $118.80   $118.80  
  Purchase #5 $223.54   5.327%   $235.448   $235.45   $235.45   $235.40  
  Purchase #6 $209.41   8.585%   $227.3878   $227.39   $227.40   $227.40  
  Purchase #7 $250.40   8.824%   $272.4953   $272.50   $272.50   $272.50  
  7 purchase totals = $1,298.11       $1,399.9547   $1,399.97   $1,400.00   $1,399.90