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 $184.90   9.652%   $202.7465   $202.75   $202.75   $202.70  
  Purchase #2 $219.46   10.751%   $243.0541   $243.05   $243.05   $243.10  
  Purchase #3 $68.53   13.164%   $77.5513   $77.55   $77.55   $77.60  
  Purchase #4 $165.64   9.645%   $181.616   $181.62   $181.60   $181.60  
  Purchase #5 $116.45   8.599%   $126.4635   $126.46   $126.45   $126.50  
  Purchase #6 $236.26   12.247%   $265.1948   $265.19   $265.20   $265.20  
  Purchase #7 $76.81   13.728%   $87.3545   $87.35   $87.35   $87.40  
  7 purchase totals = $1,068.05       $1,183.9807   $1,183.97   $1,183.95   $1,184.10