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 $60.34   4.712%   $63.1832   $63.18   $63.20   $63.20  
  Purchase #2 $65.82   12.792%   $74.2397   $74.24   $74.25   $74.20  
  Purchase #3 $158.37   7.695%   $170.5566   $170.56   $170.55   $170.60  
  Purchase #4 $144.70   5.525%   $152.6947   $152.69   $152.70   $152.70  
  Purchase #5 $136.81   7.656%   $147.2842   $147.28   $147.30   $147.30  
  Purchase #6 $156.78   6.418%   $166.8421   $166.84   $166.85   $166.80  
  Purchase #7 $76.74   7.141%   $82.22   $82.22   $82.20   $82.20  
  7 purchase totals = $799.56       $857.0205   $857.01   $857.05   $857.00