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 $212.26   8.194%   $229.6526   $229.65   $229.65   $229.70  
  Purchase #2 $6.81   13.238%   $7.7115   $7.71   $7.70   $7.70  
  Purchase #3 $241.46   7.125%   $258.664   $258.66   $258.65   $258.70  
  Purchase #4 $74.67   11.428%   $83.2033   $83.20   $83.20   $83.20  
  Purchase #5 $24.47   6.608%   $26.087   $26.09   $26.10   $26.10  
  Purchase #6 $124.68   11.237%   $138.6903   $138.69   $138.70   $138.70  
  Purchase #7 $242.54   12.797%   $273.5778   $273.58   $273.60   $273.60  
  7 purchase totals = $926.89       $1,017.5865   $1,017.58   $1,017.60   $1,017.70