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 $184.46   12.320%   $207.1855   $207.19   $207.20   $207.20  
  Purchase #2 $142.61   3.552%   $147.6755   $147.68   $147.70   $147.70  
  Purchase #3 $127.79   4.415%   $133.4319   $133.43   $133.45   $133.40  
  Purchase #4 $197.83   3.819%   $205.3851   $205.39   $205.40   $205.40  
  Purchase #5 $196.55   8.531%   $213.3177   $213.32   $213.30   $213.30  
  Purchase #6 $45.86   4.860%   $48.0888   $48.09   $48.10   $48.10  
  Purchase #7 $71.88   9.172%   $78.4728   $78.47   $78.45   $78.50  
  7 purchase totals = $966.98       $1,033.5573   $1,033.57   $1,033.60   $1,033.60