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 $88.58   8.254%   $95.8914   $95.89   $95.90   $95.90  
  Purchase #2 $48.41   13.314%   $54.8553   $54.86   $54.85   $54.90  
  Purchase #3 $221.44   13.343%   $250.9867   $250.99   $251.00   $251.00  
  Purchase #4 $112.94   7.703%   $121.6398   $121.64   $121.65   $121.60  
  Purchase #5 $59.43   6.715%   $63.4207   $63.42   $63.40   $63.40  
  Purchase #6 $146.91   10.552%   $162.4119   $162.41   $162.40   $162.40  
  Purchase #7 $30.99   6.614%   $33.0397   $33.04   $33.05   $33.00  
  7 purchase totals = $708.70       $782.2455   $782.25   $782.25   $782.20