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 $113.28   10.207%   $124.8425   $124.84   $124.85   $124.80  
  Purchase #2 $67.81   12.600%   $76.3541   $76.35   $76.35   $76.40  
  Purchase #3 $104.92   9.237%   $114.6115   $114.61   $114.60   $114.60  
  Purchase #4 $217.52   11.750%   $243.0786   $243.08   $243.10   $243.10  
  Purchase #5 $53.86   12.123%   $60.3894   $60.39   $60.40   $60.40  
  Purchase #6 $153.46   4.119%   $159.781   $159.78   $159.80   $159.80  
  Purchase #7 $218.54   10.213%   $240.8595   $240.86   $240.85   $240.90  
  7 purchase totals = $929.39       $1,019.9166   $1,019.91   $1,019.95   $1,020.00