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 $63.38   8.774%   $68.941   $68.94   $68.95   $68.90  
  Purchase #2 $246.40   8.290%   $266.8266   $266.83   $266.85   $266.80  
  Purchase #3 $96.54   5.460%   $101.8111   $101.81   $101.80   $101.80  
  Purchase #4 $236.89   13.764%   $269.4955   $269.50   $269.50   $269.50  
  Purchase #5 $241.64   10.701%   $267.4979   $267.50   $267.50   $267.50  
  Purchase #6 $133.87   13.337%   $151.7242   $151.72   $151.70   $151.70  
  Purchase #7 $124.66   11.280%   $138.7216   $138.72   $138.70   $138.70  
  7 purchase totals = $1,143.38       $1,265.0179   $1,265.02   $1,265.00   $1,264.90