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 $88.46   5.511%   $93.335   $93.34   $93.35   $93.30  
  Purchase #2 $240.58   9.178%   $262.6604   $262.66   $262.65   $262.70  
  Purchase #3 $202.38   8.482%   $219.5459   $219.55   $219.55   $219.50  
  Purchase #4 $95.46   9.443%   $104.4743   $104.47   $104.45   $104.50  
  Purchase #5 $49.80   10.531%   $55.0444   $55.04   $55.05   $55.00  
  Purchase #6 $120.39   12.163%   $135.033   $135.03   $135.05   $135.00  
  Purchase #7 $76.38   9.657%   $83.756   $83.76   $83.75   $83.80  
  7 purchase totals = $873.45       $953.8490   $953.85   $953.85   $953.80