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 $25.96   3.845%   $26.9582   $26.96   $26.95   $27.00  
  Purchase #2 $156.57   6.174%   $166.2366   $166.24   $166.25   $166.20  
  Purchase #3 $24.89   4.536%   $26.019   $26.02   $26.00   $26.00  
  Purchase #4 $43.43   12.490%   $48.8544   $48.85   $48.85   $48.90  
  Purchase #5 $189.56   3.697%   $196.568   $196.57   $196.55   $196.60  
  Purchase #6 $142.66   9.787%   $156.6221   $156.62   $156.60   $156.60  
  Purchase #7 $247.29   8.138%   $267.4145   $267.41   $267.40   $267.40  
  7 purchase totals = $830.36       $888.6728   $888.67   $888.60   $888.70