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 $24.89   7.261%   $26.6973   $26.70   $26.70   $26.70  
  Purchase #2 $83.62   5.786%   $88.4583   $88.46   $88.45   $88.50  
  Purchase #3 $42.77   7.291%   $45.8884   $45.89   $45.90   $45.90  
  Purchase #4 $52.75   4.648%   $55.2018   $55.20   $55.20   $55.20  
  Purchase #5 $224.90   4.129%   $234.1861   $234.19   $234.20   $234.20  
  Purchase #6 $91.67   7.121%   $98.1978   $98.20   $98.20   $98.20  
  Purchase #7 $230.90   6.780%   $246.555   $246.56   $246.55   $246.60  
  7 purchase totals = $751.50       $795.1847   $795.20   $795.20   $795.30