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 $152.95   9.598%   $167.6301   $167.63   $167.65   $167.60  
  Purchase #2 $89.97   4.128%   $93.684   $93.68   $93.70   $93.70  
  Purchase #3 $23.47   8.396%   $25.4405   $25.44   $25.45   $25.40  
  Purchase #4 $125.31   11.347%   $139.5289   $139.53   $139.55   $139.50  
  Purchase #5 $198.80   11.699%   $222.0576   $222.06   $222.05   $222.10  
  Purchase #6 $193.64   9.135%   $211.329   $211.33   $211.35   $211.30  
  Purchase #7 $25.66   6.620%   $27.3587   $27.36   $27.35   $27.40  
  7 purchase totals = $809.80       $887.0288   $887.03   $887.10   $887.00