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 $246.29   6.488%   $262.2693   $262.27   $262.25   $262.30  
  Purchase #2 $134.28   7.656%   $144.5605   $144.56   $144.55   $144.60  
  Purchase #3 $150.96   9.495%   $165.2937   $165.29   $165.30   $165.30  
  Purchase #4 $175.99   6.871%   $188.0823   $188.08   $188.10   $188.10  
  Purchase #5 $13.35   6.240%   $14.183   $14.18   $14.20   $14.20  
  Purchase #6 $113.59   5.153%   $119.4433   $119.44   $119.45   $119.40  
  Purchase #7 $104.68   8.277%   $113.3444   $113.34   $113.35   $113.30  
  7 purchase totals = $939.14       $1,007.1765   $1,007.16   $1,007.20   $1,007.20