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 $67.48   13.583%   $76.6458   $76.65   $76.65   $76.60  
  Purchase #2 $6.48   3.478%   $6.7054   $6.71   $6.70   $6.70  
  Purchase #3 $220.88   13.721%   $251.1869   $251.19   $251.20   $251.20  
  Purchase #4 $212.42   5.774%   $224.6851   $224.69   $224.70   $224.70  
  Purchase #5 $216.66   8.748%   $235.6134   $235.61   $235.60   $235.60  
  Purchase #6 $144.25   4.467%   $150.6936   $150.69   $150.70   $150.70  
  Purchase #7 $84.60   3.642%   $87.6811   $87.68   $87.70   $87.70  
  7 purchase totals = $952.77       $1,033.2113   $1,033.22   $1,033.25   $1,033.20