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 $156.46   6.176%   $166.123   $166.12   $166.10   $166.10  
  Purchase #2 $214.55   8.398%   $232.5679   $232.57   $232.55   $232.60  
  Purchase #3 $65.73   12.103%   $73.6853   $73.69   $73.70   $73.70  
  Purchase #4 $54.63   9.306%   $59.7139   $59.71   $59.70   $59.70  
  Purchase #5 $234.47   13.857%   $266.9605   $266.96   $266.95   $267.00  
  Purchase #6 $86.89   5.433%   $91.6107   $91.61   $91.60   $91.60  
  Purchase #7 $138.52   11.317%   $154.1963   $154.20   $154.20   $154.20  
  7 purchase totals = $951.25       $1,044.8576   $1,044.86   $1,044.80   $1,044.90