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 $220.46   12.274%   $247.5193   $247.52   $247.50   $247.50  
  Purchase #2 $232.25   10.842%   $257.4305   $257.43   $257.45   $257.40  
  Purchase #3 $5.54   8.730%   $6.0236   $6.02   $6.00   $6.00  
  Purchase #4 $239.58   8.186%   $259.192   $259.19   $259.20   $259.20  
  Purchase #5 $85.90   6.793%   $91.7352   $91.74   $91.75   $91.70  
  Purchase #6 $37.31   13.864%   $42.4827   $42.48   $42.50   $42.50  
  Purchase #7 $190.43   8.311%   $206.2566   $206.26   $206.25   $206.30  
  7 purchase totals = $1,011.47       $1,110.6399   $1,110.64   $1,110.65   $1,110.60