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 $79.53   4.313%   $82.9601   $82.96   $82.95   $83.00  
  Purchase #2 $124.69   7.704%   $134.2961   $134.30   $134.30   $134.30  
  Purchase #3 $184.58   5.578%   $194.8759   $194.88   $194.90   $194.90  
  Purchase #4 $152.69   4.621%   $159.7458   $159.75   $159.75   $159.70  
  Purchase #5 $110.79   10.665%   $122.6058   $122.61   $122.60   $122.60  
  Purchase #6 $188.74   6.820%   $201.6121   $201.61   $201.60   $201.60  
  Purchase #7 $114.83   7.717%   $123.6914   $123.69   $123.70   $123.70  
  7 purchase totals = $955.85       $1,019.7872   $1,019.80   $1,019.80   $1,019.80