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 $242.73   8.473%   $263.2965   $263.30   $263.30   $263.30  
  Purchase #2 $114.59   10.680%   $126.8282   $126.83   $126.85   $126.80  
  Purchase #3 $235.39   13.711%   $267.6643   $267.66   $267.65   $267.70  
  Purchase #4 $27.72   7.703%   $29.8553   $29.86   $29.85   $29.90  
  Purchase #5 $157.34   7.115%   $168.5347   $168.53   $168.55   $168.50  
  Purchase #6 $71.45   5.191%   $75.159   $75.16   $75.15   $75.20  
  Purchase #7 $84.77   11.700%   $94.6881   $94.69   $94.70   $94.70  
  7 purchase totals = $933.99       $1,026.0261   $1,026.03   $1,026.05   $1,026.10