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 $219.67   12.548%   $247.2342   $247.23   $247.25   $247.20  
  Purchase #2 $245.98   8.363%   $266.5513   $266.55   $266.55   $266.60  
  Purchase #3 $26.98   10.181%   $29.7268   $29.73   $29.75   $29.70  
  Purchase #4 $103.74   4.232%   $108.1303   $108.13   $108.15   $108.10  
  Purchase #5 $60.32   8.247%   $65.2946   $65.29   $65.30   $65.30  
  Purchase #6 $133.27   3.322%   $137.6972   $137.70   $137.70   $137.70  
  Purchase #7 $190.60   9.625%   $208.9453   $208.95   $208.95   $208.90  
  7 purchase totals = $980.56       $1,063.5797   $1,063.58   $1,063.65   $1,063.50