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 $88.83   8.206%   $96.1194   $96.12   $96.10   $96.10  
  Purchase #2 $175.67   8.547%   $190.6845   $190.68   $190.70   $190.70  
  Purchase #3 $103.51   13.205%   $117.1785   $117.18   $117.20   $117.20  
  Purchase #4 $246.32   12.293%   $276.6001   $276.60   $276.60   $276.60  
  Purchase #5 $95.74   13.664%   $108.8219   $108.82   $108.80   $108.80  
  Purchase #6 $177.75   8.874%   $193.5235   $193.52   $193.50   $193.50  
  Purchase #7 $69.72   8.830%   $75.8763   $75.88   $75.90   $75.90  
  7 purchase totals = $957.54       $1,058.8042   $1,058.80   $1,058.80   $1,058.80