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 $63.62   5.829%   $67.3284   $67.33   $67.35   $67.30  
  Purchase #2 $119.53   11.258%   $132.9867   $132.99   $133.00   $133.00  
  Purchase #3 $140.57   7.103%   $150.5547   $150.55   $150.55   $150.60  
  Purchase #4 $116.42   12.653%   $131.1506   $131.15   $131.15   $131.20  
  Purchase #5 $245.70   8.847%   $267.4371   $267.44   $267.45   $267.40  
  Purchase #6 $237.82   12.737%   $268.1111   $268.11   $268.10   $268.10  
  Purchase #7 $213.94   4.276%   $223.0881   $223.09   $223.10   $223.10  
  7 purchase totals = $1,137.60       $1,240.6567   $1,240.66   $1,240.70   $1,240.70