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 $110.38   5.236%   $116.1595   $116.16   $116.15   $116.20  
  Purchase #2 $209.74   11.662%   $234.1999   $234.20   $234.20   $234.20  
  Purchase #3 $6.41   9.523%   $7.0204   $7.02   $7.00   $7.00  
  Purchase #4 $63.82   4.258%   $66.5375   $66.54   $66.55   $66.50  
  Purchase #5 $236.25   6.229%   $250.966   $250.97   $250.95   $251.00  
  Purchase #6 $190.31   4.476%   $198.8283   $198.83   $198.85   $198.80  
  Purchase #7 $160.33   9.550%   $175.6415   $175.64   $175.65   $175.60  
  7 purchase totals = $977.24       $1,049.3531   $1,049.36   $1,049.35   $1,049.30