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 $49.70   5.867%   $52.6159   $52.62   $52.60   $52.60  
  Purchase #2 $229.31   8.522%   $248.8518   $248.85   $248.85   $248.90  
  Purchase #3 $228.41   11.435%   $254.5287   $254.53   $254.55   $254.50  
  Purchase #4 $71.30   5.690%   $75.357   $75.36   $75.35   $75.40  
  Purchase #5 $5.77   3.354%   $5.9635   $5.96   $5.95   $6.00  
  Purchase #6 $67.47   5.691%   $71.3097   $71.31   $71.30   $71.30  
  Purchase #7 $71.87   12.487%   $80.8444   $80.84   $80.85   $80.80  
  7 purchase totals = $723.83       $789.4710   $789.47   $789.45   $789.50