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 $148.77   13.312%   $168.5743   $168.57   $168.55   $168.60  
  Purchase #2 $207.53   9.135%   $226.4879   $226.49   $226.50   $226.50  
  Purchase #3 $163.51   3.588%   $169.3767   $169.38   $169.40   $169.40  
  Purchase #4 $101.30   4.516%   $105.8747   $105.87   $105.85   $105.90  
  Purchase #5 $149.89   10.725%   $165.9657   $165.97   $165.95   $166.00  
  Purchase #6 $22.46   11.276%   $24.9926   $24.99   $25.00   $25.00  
  Purchase #7 $143.89   6.466%   $153.1939   $153.19   $153.20   $153.20  
  7 purchase totals = $937.35       $1,014.4658   $1,014.46   $1,014.45   $1,014.60