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 $177.25   11.518%   $197.6657   $197.67   $197.65   $197.70  
  Purchase #2 $89.38   8.117%   $96.635   $96.64   $96.65   $96.60  
  Purchase #3 $136.69   5.174%   $143.7623   $143.76   $143.75   $143.80  
  Purchase #4 $70.71   12.415%   $79.4886   $79.49   $79.50   $79.50  
  Purchase #5 $163.76   9.781%   $179.7774   $179.78   $179.80   $179.80  
  Purchase #6 $226.75   12.151%   $254.3024   $254.30   $254.30   $254.30  
  Purchase #7 $247.37   12.799%   $279.0309   $279.03   $279.05   $279.00  
  7 purchase totals = $1,111.91       $1,230.6623   $1,230.67   $1,230.70   $1,230.70