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 $201.36   11.127%   $223.7653   $223.77   $223.75   $223.80  
  Purchase #2 $135.38   12.398%   $152.1644   $152.16   $152.15   $152.20  
  Purchase #3 $173.43   8.743%   $188.593   $188.59   $188.60   $188.60  
  Purchase #4 $227.41   10.776%   $251.9157   $251.92   $251.90   $251.90  
  Purchase #5 $106.26   6.656%   $113.3327   $113.33   $113.35   $113.30  
  Purchase #6 $125.45   4.858%   $131.5444   $131.54   $131.55   $131.50  
  Purchase #7 $182.91   13.351%   $207.3303   $207.33   $207.35   $207.30  
  7 purchase totals = $1,152.20       $1,268.6458   $1,268.64   $1,268.65   $1,268.60